Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity

Polymerized small molecular acceptor based all-polymer solar cells with an efficiency of 16.16% via tuning polymer blend morphology by molecular design

All-polymer solar cells (all-PSCs) based on polymerized small molecular acceptors (PSMAs) have made significant progress recently. Here, we synthesize two A-DA’D-A small molecule acceptor based PSMAs of PS-Se with benzo[c][1,2,5]thiadiazole A’-core and PN-Se with benzotriazole A’-core, for the studies of the effect of molecular structure on the photovoltaic performance of the PSMAs. The two PSMAs possess broad absorption with PN-Se showing more red-shifted absorption than PS-Se and suitable electronic energy levels for the application as polymer acceptors in the all-PSCs with PBDB-T as polymer donor. Cryogenic transmission electron microscopy visualizes the aggregation behavior of the PBDB-T donor and the PSMA in their solutions. In addition, a bicontinuous-interpenetrating network in the PBDB-T:PN-Se blend film with aggregation size of 10~20 nm is clearly observed by the photoinduced force microscopy. The desirable morphology of the PBDB-T:PN-Se active layer leads its all-PSC showing higher power conversion efficiency of 16.16%.

Through development of non-fullerene acceptors, OPVs have reached efficiencies of 18%, yet the inadequate operational lifetime still poses a challenge for the commercialisation. Here, the authors investigate the origin of instability of NFA solar cells, and propose some strategies to mitigate this issue.

Simultaneously Enhanced Efficiency and Operational Stability of Nonfullerene Organic Solar Cells via Solid-Additive-Mediated Aggregation Control

The additive strategy is widely used in optimizing the morphology of organic solar cells (OSCs). The majority of additives are liquid with high boiling points, which will be trapped within device and consequently deteriorate performance during operation. In this work, solid but volatile additives 2-(4-fluorobenzylidene)-1H-indene-1,3(2H)-dione (INB-F) and 2-(4-chlorobenzylidene)-1H-indene-1,3(2H)-dione (INB-Cl) are designed to replace the common 1,8-diiodooctane (DIO) in nonfullerene OSCs. These additives present during solution casting but evaporate after moderate heating. Molecular dynamics simulations show that they can reduce the adsorption energy to improve π-π stacking among nonfullerene acceptor (NFA) molecules, an effect that enhances light absorption and electron mobility. Both INB-F and INB-Cl enhance efficiency, with INB-F achieving a maximum efficiency of 16.7% from 15.1% of the reference PBDB-T-2F (PM6):BTP-BO-4F (Y6-BO) cell, and outperforming DIO. Remarkably, they can simultaneously enhance the operational stability, with the INB-F-treated OSC maintaining over 60% of the initial efficiency after 1000 h operation, demonstrating a T₈₀ lifetime of 523 h, which is a significant improvement over T₈₀ values of 66.2 h for the reference and 6.6 h for DIO-treated OSC. The simultaneously enhanced efficiency and operational lifetime are also effective in PM6:BTP-BO-4Cl (Y7-BO) OSCs, demonstrating a universal strategy to improve the performance of OSCs.

Sb2TeSe2 Monolayers: Promising 2D Semiconductors for Highly Efficient Excitonic Solar Cells

On the basis of density functional theory computations, we demonstrated that two-dimensional (2D) α- and β-Sb2TeSe2 monolayers are promising candidates for constructing high-efficiency heterojunction excitonic solar cells. These two 2D materials possess moderate band gaps (∼1.1 eV), which can be flexibly tuned by applying external strains. They possess high carrier mobility (∼3000 cm² V^-1 s^-1) and can absorb sunlight over the whole range of the solar spectrum. Remarkably, the α- and β-Sb2TeSe2 monolayers can form desirable type II heterostructures with HfSe2 and BiOI monolayers, respectively. The power conversion efficiencies of α-Sb₂TeSe₂/HfSe₂ and β-Sb₂TeSe₂/BiOI heterojunction excitonic solar cells can reach 22.5 and 20.3%, respectively. Since α-Sb2TeSe2 and β-Sb2TeSe2 monolayers have good stability and high synthesis feasibility, they have important applications in photovoltaic solar cell devices.

A Well-Mixed Phase Formed by Two Compatible Non-Fullerene Acceptors Enables Ternary Organic Solar Cells with Efficiency over 18.6

The ternary strategy, introducing a third component into a binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The judicious selection of an appropriate third component, without sacrificing the photocurrent and voltage output of the OSC, is of significant importance in ternary devices. Herein, highly efficient OSCs fabricated using a ternary approach are demonstrated, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. The three components show complementary absorption spectra and cascade energy alignment. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both the donor and acceptor materials, and optimizes the ternary blend morphology. Moreover, the addition of L8-BO-F into the binary blend suppresses the non-radiative recombination, thus leading to a reduced voltage loss. Consequently, concurrent increases in open-circuit voltage, short-circuit current, and fill factor are realized, resulting in an unprecedented PCE of 18.66% (certified value of 18.2%), which represents the highest efficiency values reported for both single-junction and tandem OSCs so far.

Approaching 18% efficiency of ternary organic photovoltaics with wide bandgap polymer donor and well compatible Y6 : Y6-1O as acceptor

A series of ternary organic photovoltaics (OPVs) are fabricated with one wide bandgap polymer D18-Cl as donor, and well compatible Y6 and Y6-1O as acceptor. The open-circuit-voltage (VOC ) of ternary OPVs is monotonously increased along with the incorporation of Y6-1O, indicating that the alloy state should be formed between Y6 and Y6-1O due to their excellent compatibility. The energy loss can be minimized by incorporating Y6-1O, leading to the VOC improvement of ternary OPVs. By finely adjusting the Y6-1O content, a power conversion efficiency of 17.91% is achieved in the optimal ternary OPVs with 30 wt% Y6-1O in acceptors, resulting from synchronously improved short-circuit-current density (JSC ) of 25.87 mA cm-2, fill factor (FF) of 76.92% and VOC of 0.900 V in comparison with those of D18-Cl : Y6 binary OPVs. The JSC and FF improvement of ternary OPVs should be ascribed to comprehensively optimal photon harvesting, exciton dissociation and charge transport in ternary active layers. The more efficient charge separation and transport process in ternary active layers can be confirmed by the magneto-photocurrent and impedance spectroscopy experimental results, respectively. This work provides new insight into constructing highly efficient ternary OPVs with well compatible Y6 and its derivative as acceptor.

Wide-bandgap donor polymers based on a dicyanodivinyl indacenodithiophene unit for non-fullerene polymer solar cells

A wide-bandgap polymer donor with improved efficiency plays an important role in improving the photovoltaic performance of polymer solar cells (PSCs). In this study, two novel wide-bandgap polymer donors, PBDT and PBDT-S, were designed and synthesized based on a dicyanodivinyl indacenodithiophene (IDT-CN) moiety, in which benzo[1,2-b:4,5-b']dithiophene (BDT) building blocks and IDT-CN are used as electron-sufficient and -deficient units, respectively. In our study, the PBDT and PBDT-S polymer donors exhibited similar frontier-molecular-orbital energy levels and optical properties, and both copolymers showed good miscibility with the widely used narrow-bandgap small molecular acceptor Y6. Non-fullerene polymer solar cells (NF-PSCs) based on PBDT:Y6 exhibited an impressive power conversion efficiency of 10.04% with an open circuit voltage of 0.88 V, a short-circuit current density of 22.16 mA cm-2 and a fill factor of 51.31%, where the NF-PSCs based on PBDT-S:Y6 exhibited a moderate power conversion efficiency of 6.90%. The enhanced photovoltaic performance, realized by virtue of the improved short-circuit current density, can be attributed to the slightly enhanced electron mobility, higher exciton dissociation rates, more efficient charge collection and better nanoscale phase separation of the PBDT-based device. The results of this work indicate that the IDT-CN unit is a promising building block for constructing donor polymers for high-performance organic photovoltaic cells.

Synergistic Engineering of Substituents and Backbones on Donor Polymers: Toward Terpolymer Design of High-Performance Polymer Solar Cells

Design of terpolymers via copolymerization has emerged as a potential strategy for expanding the family of high-performing donor polymers and boosting the photovoltaic performance of non-fullerene polymer solar cells (PSCs). Herein, double-ester-substituted thiophenes and thienothiophenes are incorporated as third building blocks into the donor polymer PBDB-TF, developing two groups of terpolymers with donor-acceptor 1-donor-acceptor 2 (D-A1-D-A2)-type backbones. An optimum 10% concentration of double-ester-substituted thiophene units in PBDB-TF-T10 downshifts the molecular energy and increases the dielectric constant, and delivers proper miscibility and nanostructure in blends with the high-performing acceptor Y6. These characteristics are designed to synergistically enhance the photovoltage, photocurrent, and efficiency of PSCs. The resulting power conversion efficiency (PCE) of 16.4% surpasses the conventional PBDB-TF/Y6 PSCs, and it is among the best-performing PSCs based on PBDB-TF-derived terpolymers. Gratifyingly, PBDB-TF-T10 does not show significant batch-to-batch variation and it retains high PCEs above 16% in a broad range of molecular weights. This work introduces a facile strategy to easily synthesize terpolymers in combination with Y6 for the attainment of high-performing and reproducible non-fullerene PSCs.

A Simple Dithieno[3,2-b:2',3'-d]pyrrol-Rhodanine Molecular Third Component Enables Over 16.7% Efficiency and Stable Organic Solar Cells

Organic solar cells (OSCs) can achieve greatly improved power conversion efficiency (PCE) by incorporating suitable additives in active layers. Their structure design often faces the challenge of operation generality for more binary blends. Herein, a simple dithieno[3,2-b:2',3'-d]pyrrole-rhodanine molecule (DR8) featuring high compatibility with polymer donor PM6 is developed as a cost-effective third component. By employing classic ITIC-like ITC6-4Cl and Y6 as model nonfullerene acceptors (NFAs) in PM6-based binary blends, DR8 added PM6:ITC6-4Cl blends exhibit significantly promoted energy transfer and exciton dissociation. The PM6:ITC6-4Cl:DR8 (1:1:0.1, weight ratio) OSCs contribute an exciting PCE of 14.94% in comparison to host binary devices (13.52%), while PM6:Y6:DR8 (1:1.2:0.1) blends enable 16.73% PCE with all simultaneously improved photovoltaic parameters. To the best of the knowledge, this performance is among the best for ternary OSCs with simple small molecular third components in the literature. More importantly, DR8-added ternary OSCs exhibit much improved device stability against thermal aging and light soaking over binary ones. This work provides new insight on the design of efficient third components for OSCs.

Efficient Electron Transport Layer Free Small-Molecule Organic Solar Cells with Superior Device Stability

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small-molecule electron donor (H31) based on a thiophene-substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9-bis[3-(dimethyloxidoamino)propyl]anthra[2,1,9-def:6,5,10-d'e'f ']diisoquinoline-1,3,8,10(2H,9H)-tetrone (PDINO) as the ETL. The ETL-free cells deliver a superior shelf life compared to devices with an ETL. Small-molecule donor-acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers.

Significantly Boosting Efficiency of Polymer Solar Cells by Employing a Nontoxic Halogen-Free Additive

Traditional additives like 1,8-diiodooctane and 1-chloronaphthalene were successfully utilized morphology optimization of various polymer solar cells (PSCs) in an active layer, but their toxicity brought by halogen atoms limits their corresponding large-scale manufacturing. Herein, a new nontoxic halogen-free additive named benzyl benzoate (BB) was introduced into the classic PSCs (PTB7-Th:PC₇₁BM), and an optimal power conversion efficiency (PCE) of 9.43% was realized, while there was a poor PCE for additive free devices (4.83%). It was shown that BB additives could inhibit PC₇₁BM's overaggregation, which increased the interface contact area and formed a better penetration path of an active layer. In addition, BB additives could not only boost the distribution of a PTB7-Th donor at the surface, beneficial to suppressing exciton recombination in inverted devices but also boost the crystallinity of a blend layer, which is conducive to exciton dissociation and charge transport. Our work effectively improved a device performance by using a halogen-free additive, which can be referential for industrialization.

Alcohol-Soluble Zwitterionic 4-(Dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate Small Molecule as a Cathode Modifier for Nonfullerene Acceptor-Based Organic Solar Cells

A new zwitterionic small molecule 4-(dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate (PAS), synthesized from 2-dimethylaminopyrindine (2-DMAP), was developed for the ITO cathode modifier. PAS and 2-DMAP dissolved in methanol can form a thin layer on ITO cathode by a simple spin-coating process. The heteroatom moieties in 2-DMAP (sp² and sp³ nitrogen) and PAS (sp² nitrogen and sulfonate ion) can coordinate to the ITO surface and decrease the ITO work function by the induced surface dipoles. The fullerene-based (PBDTT-FTTE:PC₇₁BM) inverted OSCs using PAS and 2-DMAP interlayer can achieve PCEs of 8.95 and 8.26%, respectively, which are superior to the devices without a modifier (PCE = 3.25%) and comparable to the corresponding ZnO-based device (PCE = 8.57%). Nevertheless, 2-DMAP, like other nitrogen-containing polymer interlayer materials, turns out to be not applicable to inverted organic solar cells (I-OSCs) with IT-4F as the n-type electron acceptor because the amino group of 2-DMAP can act as a nucleophile to attack the end-group of IT-4F at the interface. The decomposition of IT-4F by 2-DMAP was carefully proved to be via retro-aldol condensation. As a result, the device (PBDBT-F:IT-4F) modified with 2-DMAP displayed a low PCE of 7.34%. The zwitterionic PAS with reduced nucleophilicity and basicity can modify the ITO surface without decomposing IT-4F. The PBDBT-F:IT-4F-based device modified with PAS maintained a high PCE of 11.41%. Most importantly, the PAS-based device using the well-known Y6 acceptor (PBDBT-F:Y6) can achieve a PCE of 13.82%. This new interfacial material can be universally applied to I-OSCs employing various A-D-A-type acceptors installed with the electrophilic 1,1-dicyanamethylene-5,6-difluoro-3-indanone (FIC) end-group.

Additive and High-Temperature Processing Boost the Photovoltaic Performance of Nonfullerene Organic Solar Cells Fabricated with Blade Coating and Nonhalogenated Solvents

Benefitting from narrow band gap nonfullerene acceptors, continually increasing power conversion efficiency (PCE) endows organic solar cells (OSCs) with great potential for commercial application. Fabricating high-performance OSCs with potential for large-scale coating and nonhalogenated solvent processing is a necessity. Herein, we have proposed the use of nonhalogenated solvents combined with high-temperature blade coating to prepare a PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione)]):Y6 (2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)))blend active layer. The resultant OSCs deliver a PCE of 15.51% when the PM6:Y6 active layer is blade-coated at 90 °C in nonhalogenated o-xylene (o-XY) host solvent containing 1,2-dimethylnaphthalene (DMN) additive. It is found that high-temperature blade coating and nonhalogenated solvent additive DMN can suppress excessive aggregation of Y6 and enhance the crystallinity of PM6 and Y6 by regulating the dynamic process of active layer formation. Finally, an optimized blend morphology with nanofibrous phase separation and enhanced crystallinity are achieved for the PM6:Y6 active layer prepared with high-temperature blade coating and nonhalogenated o-XY:DMN solvents, which not only shortens the film-drying time but also leads to increased charge generation, transport, and collection efficiency. The 1.00 cm² OSCs prepared with high-temperature blade coating and nonhalogenated solvents exhibit a high PCE of 13.87%. This approach shows great potential for large-area fabrication of OSCs.

Nonconjugated Terpolymer Acceptors with Two Different Fused-Ring Electron-Deficient Building Blocks for Efficient All-Polymer Solar Cells

The ternary polymerization strategy of incorporating different donor and acceptor units forming terpolymers as photovoltaic materials has been proven advantageous in improving power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Herein, a series of low band gap nonconjugated terpolymer acceptors based on two different fused-ring electron-deficient building blocks (IDIC16 and ITIC) with adjustable photoelectric properties were developed. As the third component, ITIC building blocks with a larger π-conjugation structure, shorter solubilizing side chains, and red-shifted absorption spectrum were incorporated into an IDIC16-based nonconjugated copolymer acceptor PF1-TS4, which built up the terpolymers with two conjugated building blocks linked by flexible thioalkyl chain-thiophene segments. With the increasing ITIC content, terpolymers show gradually broadened absorption spectra and slightly down-shifted lowest unoccupied molecular orbital levels. The active layer based on terpolymer PF1-TS4-60 with a 60% ITIC unit presents more balanced hole and electron mobilities, higher photoluminescence quenching efficiency, and improved morphology compared to those based on PF1-TS4. In all-polymer solar cells (all-PSCs), PF1-TS4-60, matched with a wide band gap polymer donor PM6, achieved a similar open-circuit voltage (Voc) of 0.99 V, a dramatically increased short-circuit current density (Jsc) of 15.30 mA cm-2, and fill factor (FF) of 61.4% compared to PF1-TS4 (Voc = 0.99 V, Jsc = 11.21 mA cm-2, and FF = 55.6%). As a result, the PF1-TS4-60-based all-PSCs achieved a PCE of 9.31%, which is ∼50% higher than the PF1-TS4-based ones (6.17%). The results demonstrate a promising approach to develop high-performance nonconjugated terpolymer acceptors for efficient all-PSCs by means of ternary polymerization using two different A-D-A-structured fused-ring electron-deficient building blocks.

Understanding of the Nearly Linear Tunable Open-Circuit Voltages in Ternary Organic Solar Cells Based on Two Non-fullerene Acceptors

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (V_OC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of V_OC have been well-established in the binary system; however, the understanding of V_OC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased V_OC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable V_OC. Our results provide a perspective for understanding the origin of V_OC in NFA-based ternary OSCs.

From Y6 to BTPT-4F: a theoretical insight into the influence of the individual change of fused-ring skeleton length or side alkyl chains on molecular arrangements and electron mobility

Organic solar cells (OSCs) based on non-fullerene acceptor (NFA) Y6 have drawn tremendous attention due to the great progress in their power conversion efficiencies (PCEs).

Cu(ii)-Porphyrin based near-infrared molecules: synthesis, characterization and photovoltaic application

Three novel Cu(ii)-porphyrin-based near-infrared non-fullerene acceptors were developed, which show strong intramolecular charge transfer absorption spectra.

Numerical study on the angular light trapping of the energy yield of organic solar cells with an optical cavity

A limiting factor in organic solar cells (OSCs) is the incomplete absorption in the thin absorber layer. One concept to enhance absorption is to apply an optical cavity design. In this study, the performance of an OSC with cavity is evaluated. By means of a comprehensive energy yield (EY) model, the improvement is demonstrated by applying realistic sky irradiance, covering a wide range of incidence angles. The relative enhancement in EY for different locations is found to be 11-14% compared to the reference device with an indium tin oxide front electrode. The study highlights the improved angular light absorption as well as the angular robustness of an OSC with cavity.

Optimized Active Layer Morphologies via Ternary Copolymerization of Polymer Donors for 17.6 % Efficiency Organic Solar Cells with Enhanced Fill Factor

Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6-Tz20 by incorporating the 5,5'-dithienyl-2,2'-bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6-Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6-Tz20: Y6-based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance.

Precisely Controlling the Position of Bromine on the End Group Enables Well-Regular Polymer Acceptors for All-Polymer Solar Cells with Efficiencies over 15

Recent advances in the development of polymerized A-D-A-type small-molecule acceptors (SMAs) have promoted the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) over 13%. However, the monomer of an SMA typically consists of a mixture of three isomers due to the regio-isomeric brominated end groups (IC-Br(in) and IC-Br(out)). In this work, the two isomeric end groups are successfully separated, the regioisomeric issue is solved, and three polymer acceptors, named PY-IT, PY-OT, and PY-IOT, are developed, where PY-IOT is a random terpolymer with the same ratio of the two acceptors. Interestingly, from PY-OT, PY-IOT to PY-IT, the absorption edge gradually redshifts and electron mobility progressively increases. Theory calculation indicates that the LUMOs are distributed on the entire molecular backbone of PY-IT, contributing to the enhanced electron transport. Consequently, the PM6:PY-IT system achieves an excellent PCE of 15.05%, significantly higher than those for PY-OT (10.04%) and PY-IOT (12.12%). Morphological and device characterization reveals that the highest PCE for the PY-IT-based device is the fruit of enhanced absorption, more balanced charge transport, and favorable morphology. This work demonstrates that the site of polymerization on SMAs strongly affects device performance, offering insights into the development of efficient polymer acceptors for all-PSCs.

Eco-Friendly Polymer Solar Cells: Advances in Green-Solvent Processing and Material Design

Despite the recent breakthroughs of polymer solar cells (PSCs) exhibiting a power conversion efficiency of over 17%, toxic and hazardous organic solvents such as chloroform and chlorobenzene are still commonly used in their fabrication, which impedes the practical application of PSCs. Thus, the development of eco-friendly processing methods suitable for industrial-scale production is now considered an imperative research focus. This Review provides a roadmap for the design of efficient photoactive materials that are compatible with non-halogenated green solvents (e.g., xylenes, toluene, and tetrahydrofuran). We summarize the recent development of green processing solvents and the processing methods to match with the efficient photoactive materials used in non-fullerene solar cells. We further review progress in the use of more eco-friendly solvents (i.e., water or alcohol) for achieving truly sustainable and eco-friendly PSC fabrication. For example, the concept of water- or alcohol-dispersed nanoparticles made of conjugated materials is introduced. Also, recent important progress and strategies to develop water/alcohol-soluble photoactive materials that completely eliminate the use of conventional toxic solvents are discussed. Finally, we provide our perspectives on the challenges facing the current green processing methods and materials, such as large-area coating techniques and long-term stability. We believe this Review will inform the development of PSCs that are truly clean and renewable energy sources.

Structural Cutting of Non-fullerene Acceptors by Chlorination: Effects of Substituent Number on Device Performance

Effects of chlorination on photovoltaic performance of organic solar cells are yet largely unclear though it is emerging as a special yet effective strategy to design highly efficient non-fullerene acceptors (NFAs). Herein, a bi-chlorine-substituted NFA with regioregularity, namely, bichlorinated dithienothiophen[3.2-b]- pyrrolobenzothiadiazole (BTP-2Cl-δ), is synthesized and compared to the non-chlorinated BTP and tetra-chlorine-substituted BTP-4Cl to study the effects of Cl number on the photovoltaic performance. From BTP to BTP-2Cl-δ and BTP-4Cl, the three molecules show gradually red-shifted absorption peaks, narrowed band gaps, and lowered highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). Polymer solar cells are fabricated using PM6 as the donor and the three small molecules as the acceptors. From BTP to BTP-2Cl-δ, efficiencies (8.8 vs 15.4%) are significantly enhanced due to the better film morphology and strong crystallization of the BTP-2Cl-δ-based device, giving rise to boosted fill factors (FFs) and short-circuit current densities (J_SC's). From BTP-2Cl-δ to BTP-4Cl, although J_SC's (24.3 vs 25.0 mA cm^-2) are slightly elevated due to the higher crystallinity of BTP-4Cl, leading to improved exciton dissociation and collection efficiencies, FFs (71.1 vs 68.0%) are obviously decreased owing to the unfavorable film morphology, unbalanced hole-electron mobilities, and higher charge recombination in BTP-4Cl-based devices. As such, the efficiency of the BTP-2Cl-δ-based device (15.4%) is superior to that of the BTP-4Cl-based device (14.5%). This work elucidates a design strategy by cutting the numbers of substituent chlorine to obtain desired energy levels and crystallization with optimal performance.

Artificial Carbon Graphdiyne: Status and Challenges in Nonlinear Photonic and Optoelectronic Applications

The creative integration of sp-hybridized carbon atoms into artificial carbon graphdiyne has led to graphdiyne with superior properties in terms of uniformly distributed pores, ambipolar carrier transport, natural bandgap, and broadband absorption. Consequently, graphdiyne, regarded as a promising carbon material, has garnered particular attention in light-matter interactions. Light-matter interactions play an important role in optical information technology and meet the increasing demand for various energy sources. Herein, the status and challenges in nonlinear photonic and optoelectronic applications of graphdiyne, which are still in the infancy stage, are summarized. Furthermore, the bottleneck and perspective of graphdiyne in these aspects are discussed. It is therefore anticipated that this review could promote the development of graphdiyne in photonic and optoelectronic fields.

A Non-Conjugated Polymer Acceptor for Efficient and Thermally Stable All-Polymer Solar Cells

A non-conjugated polymer acceptor PF1-TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient >105  cm-1 , a high LUMO level of -3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1-TS4-based all-PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is ≈45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1-TS4-based all-PSC has good thermal stability with ≈70 % of its initial PCE retained after being stored at 85 °C for 180 h, while the IDIC16-based device only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non-conjugated thioalkyl segments.

High-Performance Ternary Polymer Solar Cells Enabled by a New Narrow Bandgap Nonfullerene Small Molecule Acceptor with a Higher LUMO Level

Obtaining a large open-circuit voltage (V_OC ) and high short-circuit current density (J_SC ) simultaneously is important in improving power conversion efficiency (PCE) of organic photovoltaics. The ternary strategy with using a higher lowest unoccupied molecular orbital (LUMO) level nonfullerene acceptor (NFA) guest can achieve increased V_OC , yet J_SC is decreased or maintained, so it's still a challenge to offer increased V_OC and J_SC values concurrently via the newly presented V_OC -increased ternary strategy. To overcome this issue, a new narrow bandgap NFA TT-S-4F is reported by introducing 3,6-dimethoxylthieno[3,2-b]thiophene (TT) as π-spacers to connect electron-rich core with terminal groups, so as to upshift the LUMO level and extend π-system. When adding 10% TT-S-4F into binary system based on PTB7-Th:IEICO-4F, the higher-LUMO-level of TT-S-4F, the increased charge mobilities, the reduced trap-assisted combination loss, and a finer nanofiber structure and increased phase separation size are obtained, which simultaneously promotes J_SC , V_OC , and fill factor (FF), thus obtaining an optimal PCE (12.5% vs 11.5%). This work illustrates that an extending conjugated backbone with large π-spacers and inclusion of alkylthiophenyl side-chains is a concept to synthesize NFA guests for use on the V_OC -increased ternary strategy that enables to realize simultaneously increased J_SC , V_OC , and FF.

A Low-Temperature Solution-Processed CuSCN/Polymer Hole Transporting Layer Enables High Efficiency for Organic Solar Cells

The hole transporting layers (HTLs) between the electrode and light absorber play a vital role in charge extraction and transport processes in organic solar cells (OSCs). Herein, a bilayer structure HTL of CuSCN/TFB is formed by soluble copper(I) thiocyanate (CuSCN) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl)))] (TFB). The excellent charge extraction capability is proved in nonfullerene PM6:Y6 and fullerene PTB7-Th:PC₇₁BM blend system-based cells. The introduction of TFB tunes the work function and polishes the interfacial contact between the HTL and light absorber, which favors the hole extraction process in cells. Meanwhile, lower recombination loss, higher exciton dissociation probability, and larger domain size are observed in CuSCN/TFB HTL-based cells compared to those of the reference cell with the pristine CuSCN HTL, which significantly improve the photovoltaic performance. As a result, a champion efficiency of 15.10% is obtained, which is >14% higher than the efficiency of 13.15% obtained in the reference cell. This study suggests that CuSCN/TFB is a promising HTL to achieve high efficiency for OSCs.

A Narrow-Bandgap n-Type Polymer with an Acceptor-Acceptor Backbone Enabling Efficient All-Polymer Solar Cells

Narrow-bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow-bandgap polymer acceptor L14, featuring an acceptor-acceptor (A-A) type backbone, is synthesized by copolymerizing a dibrominated fused-ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A-A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low-lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open-circuit voltage (V_oc ), which is attributed to a small nonradiative recombination loss (E_loss,nr ) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V_oc , an excellent efficiency of 14.3% is achieved, which is among the highest values for all-polymer solar cells (all-PSCs). The results demonstrate the superiority of narrow-bandgap A-A type polymers for improving all-PSC performance and pave a way toward developing high-performance polymer acceptors for all-PSCs.

Journey from Small-Molecule Diyne Structures to 2D Graphdiyne: Synthetic Strategies

Graphdiyne (GDY) exhibits unique characteristics of a highly conjugated π system, evenly distributed nanopores, and a direct band gap. This has encouraged multidisciplinary research groups to investigate its application in energy conversion and storage, catalysts, electronic devices, sensing, and separation. Herein, the achievements of synthetic strategies for preparing small-molecule diyne structures (GDY substructure), 1D nanoribbons, and 2D GDY are presented. These studies may help future investigations into the basic structure-related properties of GDY and synthetic methodology for the future developments of GDY-related 2D carbon materials.

Orthogonal Printable Reduced Graphene Oxide 2D Materials as Hole Transport Layers for High-Performance Inverted Polymer Solar Cells: Sheet Size Effect on Photovoltaic Properties

Creating an orthogonal printable hole-transporting layer (HTL) without damaging the underlying layer is still a major challenge in fabricating large-area printed inverted polymer solar cells (PSCs). In this study, we prepared orthogonal-processable fluorine-functionalized reduced graphene oxide (FrGO) series with various two-dimensional sheet sizes such as large-sized FrGO (1.1 μm), medium-sized FrGO (0.7 μm), and small-sized FrGO (0.3 μm) and systematically investigated the size effect of FrGOs on the hole transport properties of PSCs. The FrGOs exhibit highly stable dispersion without change over 90 days in 2-propanol solvent, indicating very high dispersion stability. Decreasing the sheet size of FrGOs enhanced hole-transporting properties, resulting in power conversion efficiencies (PCEs) of 9.27 and 9.02% for PTB7-Th:EH-IDTBR- and PTB7-Th:PC₇₁BM-based PSCs, respectively. Compared to devices with solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a 14% enhancement of PCEs was achieved. Interestingly, the PCEs of devices with the smallest FrGO sheet are higher than the PCE of 8.77% of a device with vacuum-deposited MoO₃. The enhancement in the performance of PSCs is attributed to the enhanced charge collection efficiency, decreased leakage current, internal resistance, and minimized charge recombination. Finally, small-sized FrGO HTLs were successfully coated on the photoactive layer using the spray coating method, and they also exhibited PCEs of 9.22 and 13.26% for PTB7-Th:EH-IDTBR- and PM6:Y6-based inverted PSCs, respectively.

Effect of Nitro-Substituted Ending Groups on the Photovoltaic Properties of Nonfullerene Acceptors

Chemical modification of end groups has proved to be an effective way to design new acceptor-donor-acceptor (A-D-A)-structured nonfullerene acceptors (NFAs) for high-performance organic solar cells (OSCs). Herein, we designed and synthesized two nitro-substituted end groups, N1 and N2. Using the two end groups as A units, two A-D-A acceptors, F-N1 and F-N2, were obtained. It also has been found that the nitro substitution position on end groups affects not only the absorptions and energy levels of the resultant acceptor materials but also their molecular packing behavior and active layer morphologies. In addition, the devices based on the two acceptors showed different energy losses. Power-conversion efficiencies (PCEs) of 10.66 and 11.86% were achieved for F-N1- and F-N2-based devices, respectively. This work reveals that the nitration of end groups is one of the potential strategies for designing high-performance photovoltaic active layer materials.

Substitution Effect on Thiobarbituric Acid End Groups for High Open-Circuit Voltage Non-Fullerene Organic Solar Cells

Recent advances in non-fullerene acceptors (NFAs) have resulted in significant improvement in the power conversion efficiencies (PCEs) of organic solar cells (OSCs). In our efforts to boost open-circuit voltage (V_OC) for OSCs, the molecular design employing thiobarbituric acid (TBTA) end groups and an indacenodithieno[3,2-b]thiophene (IDTT) core gives rise to NFAs with significantly raised lowest unoccupied molecular orbital (LUMO) energy level, which, when paired with PCE10, can achieve V_OC's over 1.0 V and decent PCEs that outperform the equivalent devices based on the benchmark ITIC acceptor. While the use of a TBTA end group is effective in tuning energy levels, very little is known about how the alkyl substitution on the TBTA group impacts the solar cell performance. To this end, TBTA end groups are alkylated with linear, branched, and aromatic sidechains to understand the influence on thin-film morphology and related device performances. Our study has confirmed the dependence of solar cell performance on the end-group substituents. More importantly, we reveal the presence of an ideal window of crystallinity associated with the medium-length hydrocarbon chains such as ethyl and benzyl. Deviation to the shorter methyl group makes the acceptor too crystalline to mix with the polymer donor and form proper domains, whereas longer and branched alkyl chains are too sterically bulky and hinder charge transport due to nonideal packing. Such findings underline the comprehensive nature of thin-film morphology and the subtle end-group effects for the design of non-fullerene acceptors.

A Cost-Effective, Aqueous-Solution-Processed Cathode Interlayer Based on Organosilica Nanodots for Highly Efficient and Stable Organic Solar Cells

The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large-scale production and industrial applications. In this work, an advanced aqueous-solution-processed cathode interface layer is demonstrated based on cost-effective organosilica nanodots (OSiNDs) synthesized via a simple one-step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i-OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs' interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100 mW cm^-2 ) is significantly improved by replacing the commonly used ZnO interlayer with OSiND-based interfaces.

Fast Field-Insensitive Charge Extraction Enables High Fill Factors in Polymer Solar Cells

Fill factor (FF) is a determining parameter for the power conversion efficiency (PCE) of organic solar cells (OSC). So far, nonfullerene (NF) OSCs with state-of-the-art PCEs exhibit FFs <0.8, lower than the values of Si or perovskite solar cells. The FFs directly display the dependence of photocurrent on bias, meaning that the competition between charge extraction and recombination is modulated by internal electric potential (V_in). Here, we report a study to understand key parameters/properties affecting the device FF based on seven groups of NF-OSCs consisting of widely used PBDBT-2F or PTB7-Th donors and representative NF-acceptors with FFs ranging from 0.60 to 0.78 and PCEs from 10.27 to 16.09%. We used field-dependent transient photocurrent measurements to reveal that fast and field-insensitive charge extraction at low V_in is an essential prerequisite for obtaining high FFs (0.75-0.8), which is enabled by balanced charge transport in steady and reduced bimolecular charge recombination in high purity phases. With bias-dependent quantum efficiency analysis, we further show that the recombination loss at low V_in in the devices with low FFs tends to be more significant involving excitons generated in the donor phase of blends. Our results provide relevance for how to improve the FF toward the boost of photovoltaic performance in NF-OSCs.

High-Performance Nonfullerene Organic Photovoltaics Applicable for Both Outdoor and Indoor Environments through Directional Photon Energy Transfer

With the advent of the smart factory and the Internet of Things (IoT) sensors, organic photovoltaics (OPVs) gained attention because of their ability to provide indoor power generation as an off-grid power supply. To satisfy these applications, OPVs must be capable of power generation in both outdoor and indoor at the same time for developing environmentally independent devices. For high performances in indoor irradiation, a strategy that maximizes photon utilization is essential. In this study, graphene quantum dots (GQDs), which have unique emitting properties, are introduced into a ZnO layer for efficient photon utilization of nonfullerene-based OPVs under indoor irradiation. GQDs exhibit high absorption properties in the 350-550 nm region and strong emission properties in the visible region due to down-conversion from lattice vibration. Using these properties, GQDs provide directional photon energy transfer to the bulk-heterojunction (BHJ) layer because the optical properties overlap. Additionally, the GQD-doped ZnO layer enhances shunt resistance (R_Sh) and forms good interfacial contact with the BHJ layer that results in increased carrier dissociation and transportation. Consequently, the fabricated device based on P(Cl-Cl)(BDD = 0.2) and IT-4F introduces GQDs exhibiting a maximum power conversion efficiency (PCE) of 14.0% with a superior enhanced short circuit current density (J_SC) and fill factor (FF). Furthermore, the fabricated device exhibited high PCEs of 19.6 and 17.2% under 1000 and 200 lux indoor irradiation of light emitting diode (LED) lamps, respectively.

Polyethylenimine-Ethoxylated Interfacial Layer for Efficient Electron Collection in SnO2-Based Inverted Organic Solar Cells

In this work, we studied inverted organic solar cells based on bulk heterojunction using poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C71-butyric acid methyl ester (P3HT:PCBM) as an active layer and a novel cathode buffer bilayer consisting of tin dioxide (SnO2) combined with polyethylenimine-ethoxylated (PEIE) to overcome the limitations of the single cathode buffer layer. The combination of SnO2 with PEIE is a promising approach that improves the charge carrier collection and reduces the recombination. The efficient device, which is prepared with a cathode buffer bilayer of 20 nm SnO2 combined with 10 nm PEIE, achieved Jsc = 7.86 mA/cm2, Voc = 574 mV and PCE = 2.84%. The obtained results exceed the performances of reference solar cell using only a single cathode layer of either SnO2 or PEIE.

New D-A-A'-Configured Small Molecule Donors Employing Conjugation to Red-shift the Absorption for Photovoltaics

Four new donor-acceptor-acceptor' (D-A-A')-configured donors, CPNT, DCPNT, CPNBT, and DCPNBT equipped with naphtho[1,2-c:5,6-c']bis([1,2,5]-thiadiazole) (NT) or naphtho[2,3-c][1,2,5]thiadiazole (NBT) as the central acceptor (A) unit bridging triarylamine donor (D) and cyano or dicyanovinylene acceptor (A'), were synthesized and characterized. All molecules exhibit bathochromic absorption shifts as compared to those of the benzothiadiazole (BT)-based analogues owing to improved electron-withdrawing and quinoidal character of NT and NBT cores that lead to stronger intramolecular charge transfer. Favorable energy level alignments with C₇₀ , together with the good thermal stability and the antiparallel dimeric packing render CPNT and DCPNT suitable donors for vacuum-processed organic photovoltaics (OPV)s. OPVs based on DCPNT : C₇₀ active layers displayed the best power conversion efficiency (PCE)=8.3%, along with an open circuit voltage of 0.92 V, a short circuit current of 14.5 mA cm^-2 and a fill factor of 62% under 1 sun intensity, simulated AM1.5G illumination. Importantly, continuous light-soaking with AM 1.5G illumination has verified the durability of the devices based on CPNT:C₇₀ and DCPNT : C₇₀ as the active blends. The devices were examined for their feasibility of indoor light harvesting under 500 lux illumination by a TLD-840 fluorescent lamp, giving PCE=12.8% and 12.6%, respectively. These results indicate that the NT-based D-A-A'-type donors CPNT and DCPNT are potential candidates for high-stability vacuum-processed OPVs suitable for indoor energy harvesting.

Enhanced and Balanced Charge Transport Boosting Ternary Solar Cells Over 17% Efficiency

Ternary architecture is one of the most effective strategies to boost the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, an OSC with a ternary architecture featuring a highly crystalline molecular donor DRTB-T-C4 as a third component to the host binary system consisting of a polymer donor PM6 and a nonfullerene acceptor Y6 is reported. The third component is used to achieve enhanced and balanced charge transport, contributing to an improved fill factor (FF) of 0.813 and yielding an impressive PCE of 17.13%. The heterojunctions are designed using so-called pinning energies to promote exciton separation and reduce recombination loss. In addition, the preferential location of DRTB-T-C4 at the interface between PM6 and Y6 plays an important role in optimizing the morphology of the active layer.

Conformation-Tuning Effect of Asymmetric Small Molecule Acceptors on Molecular Packing, Interaction, and Photovoltaic Performance

Understanding the conformation effect on molecular packing, miscibility, and photovoltaic performance is important to open a new avenue for small-molecule acceptor (SMA) design. Herein, two novel acceptor-(donor-acceptor1-donor)-acceptor (A-DA1D-A)-type asymmetric SMAs are developed, namely C-shaped BDTP-4F and S-shaped BTDTP-4F. The BDTP-4F-based polymer solar cells (PSCs) with PM6 as donor, yields a power conversion efficiency (PCE) of 15.24%, significantly higher than that of the BTDTP-4F-based device (13.12%). The better PCE for BDTP-4F-based device is mainly attributed to more balanced charge transport, weaker bimolecular recombination, and more favorable morphology. Additionally, two traditional A-D-A-type SMAs (IDTP-4F and IDTTP-4F) are also synthesized to investigate the conformation effect on morphology and device performance. Different from the device result above, here, IDTP-4F with S-shape conformation outperforms than IDTTP-4F with C-shape conformation. Importantly, it is found that for these two different types of SMA, the better performing binary blend has similar morphological characteristics. Specifically, both PM6:BDTP-4F and PM6:IDTP-4F blend exhibit perfect nanofibril network structure with proper domain size, obvious face-on orientation and enhance donor-acceptor interactions, thereby better device performance. This work indicates tuning molecular conformation plays pivotal role in morphology and device effciciency, shining a light on the molecular design of the SMAs.

Subtle Morphology Control with Binary Additives for High-Efficiency Non-Fullerene Acceptor Organic Solar Cells

Adding an additive is one of the effective strategies to fine-tune active layer morphology and improve performance of organic solar cells. In this work, a binary additive 1,8-diiodooctane (DIO) and 2,6-dimethoxynaphthalene (DMON) to optimize the morphology of PBDB-T:TTC8-O1-4F-based devices is reported. With the binary additive, a power conversion efficiency (PCE) of 13.22% was achieved, which is higher than those of devices using DIO (12.05%) or DMON (11.19%) individually. Comparison studies demonstrate that DIO can induce the acceptor TTC8-O1-4F to form ordered packing, while DMON can inhibit excessive aggregation of the donor and acceptor. With the synergistic effect of these two additives, the PBDB-T:TTC8-O1-4F blend film with DIO and DMON exhibits a suitable phase separation and crystallite size, leading to a high short-circuit current density (J_sc) of 23.04 mA·cm^-2 and a fill factor of 0.703 and thus improved PCE.

Cathode engineering with perylene-diimide interlayer enabling over 17% efficiency single-junction organic solar cells

In organic solar cells (OSCs), cathode interfacial materials are generally designed with highly polar groups to increase the capability of lowering the work function of cathode. However, the strong polar group could result in a high surface energy and poor physical contact at the active layer surface, posing a challenge for interlayer engineering to address the trade-off between device stability and efficiency. Herein, we report a hydrogen-bonding interfacial material, aliphatic amine-functionalized perylene-diimide (PDINN), which simultaneously down-shifts the work function of the air stable cathodes (silver and copper), and maintains good interfacial contact with the active layer. The OSCs based on PDINN engineered silver-cathode demonstrate a high power conversion efficiency of 17.23% (certified value 16.77% by NREL) and high stability. Our results indicate that PDINN is an effective cathode interfacial material and interlayer engineering via suitable intermolecular interactions is a feasible approach to improve device performance of OSCs.

Effects of the Isomerized Thiophene-Fused Ending Groups on the Performances of Twisted Non-Fullerene Acceptor-Based Polymer Solar Cells

Recently, benefiting from the merits of small-molecule acceptors (NFAs), polymer solar cells (PSCs) have achieved tremendous advances. From the perspective of the structural characteristics of the π-conjugated acceptor-donor-acceptor (A-D-A) type of organic molecules, the backbone's planarity and the terminal groups and their substituents have strong influences on the performances of the constructed NFAs. Through enlarging the dihedral angle of the conjugated main chain of NFAs, a certain degree of enhancement of photovoltaic parameters has been achieved. To further probe the influences of ending groups on the performances of nonplanar NFAs, we synthesized two new NFAs i-cc23 and i-cc34 with isomerized thiophene-fused ending groups and a twisted π-conjugated main chain. Compared to i-cc23 containing the 2-(6-oxo-5,6-dihydro-4H-cyclopenta[b]thiophen-4-ylidene)malononitrile ending group, the acceptor i-cc34 containing 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile has a relatively higher molar extinction coefficient, bathochromic-shifted absorption spectrum, and deepened energy levels. When mixed with PBDB-T in solar cells, the i-cc23-based device achieved an excellent open-circuit voltage (V_OC) of 1.10 V and a moderate power conversion efficiency of 7.34%. Although the V_OC of the i-cc34-related device was decreased to 0.96 V, the short-circuit current density and fill factor were improved, giving rise to an enhanced efficiency of 9.51%. Apart from the distinct photovoltaic performances, the two isomer-based devices exhibit a high radiative efficiency of 8 × 10^-4, leading to a very small nonradiative loss of 0.19 V. Our results emphasize the importance of the isomerized thiophene-fused ending groups on the performances of nonplanar NFA-based PSCs.