Ultra-high open-circuit voltage of perovskite solar cells induced by nucleation thermodynamics on rough substrates

Suppressing interfacial nucleation competition through supersaturation regulation for enhanced perovskite film quality and scalability

The growing interest in cost-effective and high-performing perovskite solar cells (PSCs) has driven extensive research. However, the challenge lies in upscaling PSCs while maintaining high performance. This study focuses on achieving uniform and compact perovskite films without pinholes and interfacial voids during upscaling from small PSCs to large-area modules. Competition in nucleation at concavities with various angles on rough-textured substrates during the gas-pumping drying process, coupled with different drying rates across the expansive film, aggravates these issues. Consequently, substrate roughness notably influences the deposition window of compact large-area perovskite films. We propose a supersaturation regulation approach aimed at achieving compact deposition of high-quality perovskite films over large areas. This involves introducing a rapid drying strategy to induce a high-supersaturation state, thereby equalizing nucleation across diverse concavities. This breakthrough enables the production of perovskite photovoltaics with high efficiencies of 25.58, 21.86, and 20.62% with aperture areas of 0.06, 29, and 1160 square centimeters, respectively.

Simulation and optimization of 30.17% high performance N-type TCO-free inverted perovskite solar cell using inorganic transport materials

Perovskite solar cells (PSCs) have gained much attention in recent years because of their improved energy conversion efficiency, simple fabrication process, low processing temperature, flexibility, light weight, and low cost of constituent materials when compared with their counterpart silicon based solar cells. Besides, stability and toxicity of PSCs and low power conversion efficiency have been an obstacle towards commercialization of PSCs which has attracted intense research attention. In this research paper, a Glass/Cu2O/CH3NH3SnI3/ZnO/Al inverted device structure which is made of cheap inorganic materials, n-type transparent conducting oxide (TCO)-free, stable, photoexcited toxic-free perovskite have been carefully designed, simulated and optimized using a one-dimensional solar cell capacitance simulator (SCAPS-1D) software. The effects of layers' thickness, perovskite's doping concentration and back contact electrodes have been investigated, and the optimized structure produced an open circuit voltage (Voc) of 1.0867 V, short circuit current density (JSC) of 33.4942 mA/cm2, fill factor (FF) of 82.88% and power conversion efficiency (PCE) of 30.17%. This paper presents a model that is first of its kind where the highest PCE performance and eco-friendly n-type TCO-free inverted CH3NH3SnI3 based perovskite solar cell is achieved using all-inorganic transport materials.

Pivotal avenue for hybrid electron transport layer-based perovskite solar cells with improved efficiency

This study conducted a simulative analysis of different hybrid perovskite solar cells with various hybrid electron transport layers (ETL) and hole transport layers (HTL). The electron transport layer boosts durability, lowers production costs, increases stability, improves light absorption, and increases efficiency. Hybrid ETLs are taken into consideration to improve the device's performance. The selected hybrid ETLs (PCBM-SnS2, TiO2-SnO2, and PCBM-PCPB) were modeled with four hybrid perovskite absorbers (CsPbI3, FAPbI3, MAPbI3, and FAMAPbI3) and five HTLs (PEDOT: PSS, CuI, Spiro-OMeTAD, CBTS, and NiO). Three sets of solar cells are found to be the most effective configurations after investigating over sixty different combinations of perovskite solar cell architectures. The structures show CBTS as the efficient HTL for FAMAPbI3 with all three hybrid ETLs. Besides, a holistic analysis of the effect of several factors such as the defect density and thickness of the absorber layer, temperature, parasitic resistances, capacitance, Mott-Schottky, impedance, conduction band offset, and current density-voltage and quantum efficiency characteristics is performed. The results show a maximum power conversion efficiency of 25.57%, 26.35%, and 23.36% with PCBM-SnS2, TiO2-SnO2, and PCBM-PCPB respectively. Among the studied hybrid ETLs, perovskite solar cell associated with TiO2-SnO2 has depicted a superior performance (Voc = 1.12 V, Jsc = 26.88 mA/cm2, FF = 87.27%). The efficiency of the perovskite solar cell using this study has been drastically enhanced compared to the previous experimental report. The proposed strategy provides a new avenue for attaining clean energy and allows researchers to pave the way for further design optimization to obtain high-performance solar cell devices.

A Newly Crosslinked-double Network PEDOT:PSS@PEGDMA toward Highly-Efficient and Stable Tin-Lead Perovskite Solar Cells

Until now, poly(3,4-ethylenedioxythiophene):poly(styrensulfonate) (PEDOT:PSS) is widely used in Sn-Pb perovskite solar cells (PSCs) due to its many advantages, including high optical transparency, suitable conductivity, superior wettability, and so on. However, the acidic and hydroscopic properties of the PSS component, as well as the incongruous energy level of the hole transport layer (HTL), may lead to unsatisfying interface properties and decreased device performance. Herein, by adding polyethylene glycol dimethacrylate (PEGDMA) into PEDOT:PSS, a newly crosslinked-double-network obtain of PEDOT:PSS@PEGDMA film, which could not only optimize nucleation and crystallinity of Sn-Pb perovskite films, but also suppress defect density and optimize energy level alignment at the HTL/perovskite interface. As a result, the achieves highly efficient and stable mixed Sn-Pb PSCs with an encouraging power conversion efficiency of 20.9%. Additionally, the device can maintain good stability under N2 atmosphere.

Combined DFT, SCAPS-1D, and wxAMPS frameworks for design optimization of efficient Cs2BiAgI6-based perovskite solar cells with different charge transport layers

In this study, combined DFT, SCAPS-1D, and wxAMPS frameworks are used to investigate the optimized designs of Cs2BiAgI6 double perovskite-based solar cells. First-principles calculations are employed to investigate the structural stability, optical responses, and electronic contribution of the constituent elements in Cs2BiAgI6 absorber material, where SCAPS-1D and wxAMPS simulators are used to scrutinize different configurations of Cs2BiAgI6 solar cells. Here, PCBM, ZnO, TiO2, C60, IGZO, SnO2, WS2, and CeO2 are used as ETL, and Cu2O, CuSCN, CuSbS2, NiO, P3HT, PEDOT:PSS, spiro-MeOTAD, CuI, CuO, V2O5, CBTS, CFTS are used as HTL, and Au is used as a back contact. About ninety-six combinations of Cs2BiAgI6-based solar cell structures are investigated, in which eight sets of solar cell structures are identified as the most efficient structures. Besides, holistic investigation on the effect of different factors such as the thickness of different layers, series and shunt resistances, temperature, capacitance, Mott-Schottky and generation-recombination rates, and J-V (current-voltage density) and QE (quantum efficiency) characteristics is performed. The results show CBTS as the best HTL for Cs2BiAgI6 with all eight ETLs used in this work, resulting in a power conversion efficiency (PCE) of 19.99%, 21.55%, 21.59%, 17.47%, 20.42%, 21.52%, 14.44%, 21.43% with PCBM, TiO2, ZnO, C60, IGZO, SnO2, CeO2, WS2, respectively. The proposed strategy may pave the way for further design optimization of lead-free double perovskite solar cells.

Stabilization of Perovskite Solar Cells: Recent Developments and Future Perspectives

Exceptional power conversion efficiency (PCE) of 25.7% in perovskite solar cells (PSCs) has been achieved, which is comparable with their traditional rivals (Si-based solar cells). However, commercialization-worthy efficiency and long-term stability remain a challenge. In this regard, there are increasing studies focusing on the interface engineering in PSC devices to overcome their poor technical readiness. Herein, the roles of electrode materials and interfaces in PSCs are discussed in terms of their PCEs and perovskite stability. All the current knowledge on the factors responsible for the rapid intrinsic and external degradation of PSCs is presented. Then, the roles of carbonaceous materials as substitutes for noble metals are focused on, along with the recent research progress in carbon-based PSCs. Furthermore, a sub-category of PSCs, that is, flexible PSCs, is considered as a type of exceptional power source due to their high power-to-weight ratios and figures of merit for next-generation wearable electronics. Last, the future perspectives and directions for research in PSCs are discussed, with an emphasis on their commercialization.

Attributes of High-Performance Electron Transport Layers for Perovskite Solar Cells on Flexible PET versus on Glass

Electron transport layers (ETLs) play a fundamental role in perovskite solar cells (PSCs) through charge extraction. Here, we developed flexible PSCs on 12 different kinds of ETLs based on SnO₂. We show that ETLs need to be specifically developed for plastic substrates in order to attain 15% efficient flexible cells. Recipes developed for glass substrates do not typically transfer directly. Among all the ETLs, ZnO/SnO₂ double layers delivered the highest average power conversion efficiency of 14.6% (best cell 14.8%), 39% higher than that of flexible cells of the same batch based on SnO₂-only ETLs. However, the cells with a single ETL made of SnO₂ nanoparticles were found to be more stable as well as more efficient and reproducible than SnO₂ formed from a liquid precursor (SnO₂-LP). We aimed at increasing the understanding of what makes a good ETL on polyethylene terephthalate (PET) substrates. More so than ensuring electron transport (as seen from on-current and series resistance analysis), delivering high shunt resistances (R _SH) and lower recombination currents (I _off) is key to obtain high efficiency. In fact, R _SH of PSCs fabricated on glass was twice as large, and I _off was 76% lower in relative terms, on average, than those on PET, indicating considerably better blocking behavior of ETLs on glass, which to a large extent explains the differences in average PCE (+29% in relative terms for glass vs PET) between these two types of devices. Importantly, we also found a clear trend for all ETLs and for different substrates between the wetting behavior of each surface and the final performance of the device, with efficiencies increasing with lower contact angles (ranging between ∼50 and 80°). Better wetting, with average contact angles being lower by 25% on glass versus PET, was conducive to delivering higher-quality layers and interfaces. This cognizance can help further optimize flexible devices and close the efficiency gap that still exists with their glass counterparts.

High-Performance Near-Infrared Photodetectors Based on the Synergy Effect of Short Wavelength Light Filter and Long Wavelength Response of a Perovskite/Polymer Hybrid Structure

Near-infrared photodetectors (NIR-PDs) are widely used in communications, biomedical imaging, and national defense. Here we report a new strategy to prepare a short wavelength light filter based NIR-PDs by introducing an interface layer between the perovskite layer and the polymer layer to achieve the selective passage of carriers. Through the synergistic effect of the perovskite and the interface layer, the short wavelength light component in the signal spectrum is effectively filtered out. The organic polymer layer with a bulk heterojunction structure is applied to realize the absorption and conversion of near-infrared light. The prepared device achieves a maximum external quantum efficiency of 83.7% without bias, a high specific detectivity of 1.52 × 10¹³ Jones, an NIR responsivity of 0.577A/W, and a short response time of 1.73/0.97 μs within the detection range from 770 to 900 nm. All these properties show great advantages compared with other perovskite/polymer hybrid NIR photodetectors that have been reported. This innovative strategy provides a new way to prepare high-performance near-infrared photodetectors.

Cotton soot derived carbon nanoparticles for NiO supported processing temperature tuned ambient perovskite solar cells

The emergence of perovskite solar cells (PSCs) in a "catfish effect" of other conventional photovoltaic technologies with the massive growth of high-power conversion efficiency (PCE) has given a new direction to the entire solar energy field. Replacing traditional metal-based electrodes with carbon-based materials is one of the front-runners among many other investigations in this field due to its cost-effective processability and high stability. Carbon-based perovskite solar cells (c-PSCs) have shown great potential for the development of large scale photovoltaics. First of its kind, here we introduce a facile and cost-effective large scale carbon nanoparticles (CNPs) synthesis from mustard oil assisted cotton combustion for utilization in the mesoporous carbon-based perovskite solar cell (PSC). Also, we instigate two different directions of utilizing the carbon nanoparticles for a composite high temperature processed electrode (HTCN) and a low temperature processed electrode (LTCN) with detailed performance comparison. NiO/CNP composite thin film was used in high temperature processed electrodes, and for low temperature processed electrodes, separate NiO and CNP layers were deposited. The HTCN devices with the cell structure FTO/c-TiO2/m-TiO2/m-ZrO2/high-temperature NiO-CNP composite paste/infiltrated MAPI (CH3NH3PbI3) achieved a maximum PCE of 13.2%. In addition, high temperature based carbon devices had remarkable stability of ~ 1000 h (ambient condition), retaining almost 90% of their initial efficiency. In contrast, LTCN devices with configuration FTO/c-TiO2/m-TiO2/m-ZrO2/NiO/MAPI/low-temperature CNP had a PCE limit of 14.2%, maintaining ~ 72% of the initial PCE after 1000 h. Nevertheless, we believe this promising approach and the comparative study between the two different techniques would be highly suitable and adequate for the upcoming cutting-edge experimentations of PSC.

Precise Control of Perovskite Crystallization Kinetics via Sequential A-Site Doping

Two-step-fabricated FAPbI₃ -based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI₃ -based perovskite film with sequential A-site doping of Cs⁺ and GA⁺ is revealed by in situ X-ray scattering and first-principles calculations. Incorporating Cs⁺ in the first step induces an alternative pathway from δ-CsPbI₃ to perovskite α-phase, which is energetically more favorable than the conventional pathways from PbI₂ . However, pinholes are formed due to the nonuniform nucleation with sparse δ-CsPbI₃ crystals. Fortunately, incorporating GA⁺ in the second step can not only promote the phase transition from δ-CsPbI₃ to the perovskite α-phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two-step process over the one-step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.

Surfactant-assisted doctor-blading-printed FAPbBr3 films for efficient semitransparent perovskite solar cells

Organic-inorganic hybrid perovskite solar cells have generated wide interest due to the rapid development of their photovoltaic conversion efficiencies. However, the majority of the reported devices have been fabricated via spin coating with a device area of < 1 cm². In this study, we fabricated a wide-bandgap formamidinium lead bromide (FAPbBr₃) film using a cost-effective, high-yielding doctor-blade-coating process. The effects of different surfactants, such as 1-α-phosphatidylcholine, polyoxyethylene sorbitan monooleate, sodium lauryl sulfonate, and hexadecyl trimethyl ammonium bromide, were studied during the printing process. Accompanying the optimization of the blading temperature, crystal sizes of over 10 µm and large-area perovskite films of 5 cm × 5 cm were obtained using this method. The printed FAPbBr₃ solar cells exhibited a short-circuit current density of 8.22 mA/cm², an open-circuit voltage of 1.175 V, and an efficiency of 7.29%. Subsequently, we replaced the gold with silver nanowires as the top electrode to prepare a semitransparent perovskite solar cell with an average transmittance (400-800 nm) of 25.42%, achieving a high-power efficiency of 5.11%. This study demonstrates efficient doctor-blading printing for preparing large-area FAPbBr₃ films that possess high potential for applications in building integrated photovoltaics.

Highly efficient inverted perovskite solar cells incorporating P3CT-Rb as a hole transport layer to achieve a large open circuit voltage of 1.144 V

Poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT) has been noticed as a promising hole transport layer (HTL) for high-performance inverted planar perovskite solar cells (PSCs) due to its excellent stability and relatively high hole mobility. As we all know, the morphology of perovskite films is largely influenced by the substrate materials. Considering the affinity of alkali metal ions Rb⁺ and Cs⁺ with perovskite materials, inverted perovskite solar cells using alkali metal ion (Rb⁺, Cs⁺) doped P3CT (denoted as P3CT-Rb and P3CT-Cs) as the HTLs were investigated in this work. It turned out that the work function (WF) of P3CT-Rb matches well with the valence band of perovskites. The perovskite (MAPbI_3-xCl_x) film deposited on top of the P3CT-Rb film exhibited a dense and uniform morphology with superior crystallinity and few pinholes. Consequently, a high efficiency of 20.52% was achieved for P3CT-Rb HTL-based devices, with an impressive open-circuit voltage (V_oc) of 1.144 V and a high fill factor (FF) of 82.78%.

Over 20% Efficiency in Methylammonium Lead Iodide Perovskite Solar Cells with Enhanced Stability via "in Situ Solidification" of the TiO2 Compact Layer

In methylammonium lead iodide (MAPbI₃) perovskite solar cells (PSCs), the device performance is strongly influenced by the TiO₂ electron transport layer (ETL). Typically, the ETL needs to simultaneously be thin and pinhole-free to have high transmittance and avoid shunting. In this work, we develop an "in situ solidification" process following spin coating in which the titanium-based precursor (titanium(diisopropoxide) bis(2,4-pentanedionate)) is dried under vacuum to rapidly achieve continuous TiO₂ layers. We refer to this as "gas-phase quenching". This results in thin (60 ± 10 nm), uniform, and pinhole-free TiO₂ films. The PSCs based on the gas-phase quenched TiO₂ exhibits improved power conversion efficiency, with a median value of 18.23% (champion value of 20.43%), compared to 9.03 and 14.09% for the untreated devices. Gas-phase quenching is further shown to be effective in enabling efficient charge transfer at the MAPbI₃/TiO₂ heterointerface. Furthermore, the stability of the gas-phase quenched devices is enhanced in ambient air as well as under 1 sun illumination. In addition, we achieve 12.1% efficiency in upscaled devices (1.1 cm² active area).

Photo-annealed amorphous titanium oxide for perovskite solar cells

Electron selective layers are important to the efficiency, stability and hysteresis of perovskite solar cells. Photo-annealing is a low-cost, roll-to-roll-compatible process that can be applied to the post-treatment fabrication of sol-gel based metal oxide layers. Here, we fabricate an amorphous titanium oxide electron selective layer at a low temperature in a dry atmosphere using a UV light annealing system and compare it with a thermal annealing process. Active oxygen species are created by using UV light to promote hydrolysis and condense the TiO₂ precursor, which removes organic ligands effectively. The photo-annealed TiO₂-based perovskite solar cell has a power conversion efficiency of 19.37% without hysteresis.

Molecular Design Strategy in Developing Titanyl Phthalocyanines as Dopant-Free Hole-Transporting Materials for Perovskite Solar Cells: Peripheral or Nonperipheral Substituents?

We demonstrate a molecular design strategy to enhance the efficiency of phthalocyanine (Pc)-based hole-transporting materials (HTMs) in perovskite solar cells (PSCs). Herein, two titanyl phthalocyanine (TiOPc) derivatives are designed and applied as dopant-free HTMs in planar n-i-p-structured PSCs. The newly developed TiOPc compounds possess eight n-hexylthio groups attached to either peripheral (P-SC₆-TiOPc) or nonperipheral (NP-SC₆-TiOPc) positions of the Pc ring. Utilizing these dopant-free HTMs in PSCs with a mixed cation perovskite as the light-absorbing material and tin oxide (SnO₂) as the electron-transporting material (ETM) results in a considerably enhanced efficiency for NP-SC₆-TiOPc-based devices compared to PSCs using P-SC₆-TiOPc. Hence, all of the photovoltaic parameters, including power conversion efficiency (PCE), fill factor, open-circuit voltage, and short-circuit current density, are remarkably improved from 5.33 ± 1.01%, 33.34 ± 3.45%, 0.92 ± 0.18 V, and 17.33 ± 2.08 mA cm^-2 to 15.83 ± 0.44%, 69.03 ± 1.59%, 1.05 ± 0.01 V, and 21.80 ± 0.36 mA cm^-2, respectively, when using the nonperipheral-substituted TiOPc derivative as the HTM in a PSC. Experimental and computational analysis suggests more compact molecular packing for NP-SC₆-TiOPc than P-SC₆-TiOPc in the solid state due to stronger π-π interactions, leading to thin films with better quality and higher performance in hole extraction and transportation. PSCs with NP-SC₆-TiOPc also offer much higher long-term stability than P-SC₆-TiOPc-based devices under ambient conditions with a relative humidity of 75%.

Stable Triple-Cation (Cs+-MA+-FA+) Perovskite Powder Formation under Ambient Conditions for Hysteresis-Free High-Efficiency Solar Cells

Organometallic halide perovskite materials have promising photovoltaic properties and emerged as a cost-effective solar cell technology. However, a synthesis protocol to fabricate high-quality perovskite thin films under ambient conditions remains a critical issue and hinders commercialization of the technology. Therefore, this paper proposes efficient and stable fabrication of triple-cation perovskite photoactive solid-state thin film for solar cells using preformed perovskite powder under ambient conditions. Highly crystalline triple-cation perovskite powder was synthesized by a solution-processed antisolvent recrystallization technique, and films were prepared following a previously reported recipe for an efficient triple-cation perovskite. The synthesized perovskite powder was characterized using UV-visible absorption spectroscopy, X-ray diffraction, time-resolved photoluminescence, and field emission scanning electron microscopy. Fabricated solar cells were investigated for photovoltaic characteristics, including current density-voltage hysteresis, recombination losses, and thermal stability. The improved photovoltaic characteristics and thermal stability were attributed to the superior perovskite film quality and crystalline properties.

Facile NiOx Sol-Gel Synthesis Depending on Chain Length of Various Solvents without Catalyst for Efficient Hole Charge Transfer in Perovskite Solar Cells

Nickel oxide (NiO_x)–based perovskite solar cells (PSCs) have recently gained considerable interest, and exhibit above 20% photovoltaic efficiency. However, the reported syntheses of NiO_x sol-gel used toxic chemicals for the catalysts during synthesis, which resulted in a high-temperature annealing requirement to remove the organic catalysts (ligands). Herein, we report a facile “NiO_x sol-gel depending on the chain length of various solvents” method that eschews toxic catalysts, to confirm the effect of different types of organic solvents on NiO_x synthesis. The optimized conditions of the method resulted in better morphology and an increase in the crystallinity of the perovskite layer. Furthermore, the use of the optimized organic solvent improved the absorbance of the photoactive layer in the PSC device. To compare the electrical properties, a PSC was prepared with a p-i-n structure, and the optimized divalent alcohol-based NiO_x as the hole transport layer. This improved the charge transport compared with that for the typical 1,2-ethanediol (ethylene glycol) used in earlier studies. Finally, the optimized solvent-based NiO_x enhanced device performance by increasing the short-circuit current density (J_sc), open-circuit voltage (V_oc), and fill factor (FF), compared with those of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)–based devices.

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO2

Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO₂) electron-transport layer. The Fermi level of EDTA-complexed SnO₂ is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO₂. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO₂ increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO₂ enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO₂ degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm⁻².

The development of high efficiency planar-type perovskite solar cell has been lagging behind the mesoporous-type counterpart. Here Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability.

ZnO-Assisted Growth of CH3NH3PbI3- xCl x Film and Efficient Planar Perovskite Solar Cells with a TiO2/ZnO/C60 Electron Transport Trilayer

Appropriate electron transport layers (ETL) are essential in perovskite solar cells (PSCs) with high power conversion efficiency (PCE). Herein, a TiO₂/ZnO/C₆₀ trilayer fabricated on a transparent fluorine-doped tin oxide (FTO) glass substrate is used as a compound ETL in planar PSCs. The trilayer shows positive effects on both perovskite synthesis and device performance. The ZnO layer assists growth of CH₃NH₃PbI_{3- x}Cl _x ( x ≈ 0) annealed at a lower temperature and with a shorter time, which is due to a more rapid and easier decomposition of the intermediate CH₃NH₃PbCl₃ phase in the growth of CH₃NH₃PbI_{3- x}Cl _x. All three materials in the trilayer are important for obtaining PSCs with a high PCE. ZnO is critical for enhancing the open circuit voltage by ensuring proper energy alignment with the TiO₂ and C₆₀ layers. C₆₀ enhances carrier extraction from the CH₃NH₃PbI_{3- x}Cl _x layer. TiO₂ eliminates charge recombination at the FTO surface and ensures efficient electron collection. The best-performing PSC based on the TiO₂/ZnO/C₆₀ electron transport trilayer features a PCE of 18.63% with a fill factor of 79.12%. These findings help develop an understanding of the effects of ZnO-containing ETLs on perovskite film synthesis and show promise for the future development of high-performance PSCs with compound ETLs.

Mixed Sn-Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air

Lead-based perovskite solar cells have gained ground in recent years, showing efficiency as high as 20%, which is on par with that of silicon solar cells. However, the toxicity of lead makes it a nonideal candidate for use in solar cells. Alternatively, tin-based perovskites have been proposed because of their nontoxic nature and abundance. Unfortunately, these solar cells suffer from low efficiency and stability. Here, we propose a new type of perovskite material based on mixed tin and germanium. The material showed a band gap around 1.4-1.5 eV as measured from photoacoustic spectroscopy, which is ideal from the perspective of solar cells. In a solar cell device with inverted planar structure, pure tin perovskite solar cell showed a moderate efficiency of 3.31%. With 5% doping of germanium into the perovskite, the efficiency improved up to 4.48% (6.90% after 72 h) when measured in air without encapsulation.

Revealing the Chemistry between Band Gap and Binding Energy for Lead-/Tin-Based Trihalide Perovskite Solar Cell Semiconductors

A relationship between reported experimental band gaps (solid) and DFT-calculated binding energies (gas) is established, for the first time, for each of the four ten-membered lead (or tin) trihalide perovskite solar cell semiconductor series examined in this study, including CH₃ NH₃ PbY₃ , CsPbY₃ , CH₃ NH₃ SnY₃ and CsSnY₃ (Y=I_(3-x) Br_x=1-3 , I_(3-x) Cl_x=1-3 , Br_(3-x) Cl _x=1-3 , and IBrCl). The relationship unequivocally provides a new dimension for the fundamental understanding of the optoelectronic features of solid-state solar cell thin films by using the 0 K gas-phase energetics of the corresponding molecular building blocks.