Large-area Flexible Organic Solar Cells: Printing Technologies and Modular Design

The Conjugated/Non-Conjugated Linked Dimer Acceptors Enable Efficient and Stable Flexible Organic Solar Cells

The fabrication of the flexible devices with excellent photovoltaic performance and stability is critical for the commercialization of organic solar cells (OSCs). Herein, the conjugated dimer acceptor DY-TVCl and the non-conjugated dimer acceptor DY-3T based on the monomer MY-BO are synthesized to regulate the molecular glass transition temperatures (Tg) for improving the morphology stability of active layer films. And the crack onset strain values for the blend films based on dimer acceptors are superior than that of small molecule, which are beneficial for the preparation of flexible devices. Accordingly, the binary device based on PM6:DY-TVCl achieves a maximum power conversion efficiency (PCE) of 18.01%. Meanwhile, the extrapolated T80 (time to reach 80% of initial PCE) lifetimes of the PM6:DY-TVCl-based device and PM6:DY-3T-based device are 3091 and 2227 h under 1-sun illumination, respectively, which are better than that of the PM6:MY-BO-based device (809 h). Furthermore, the flexible devices based on DY-TVCl and DY-3T exhibit the efficiencies of 15.23% and 14.34%, respectively. This work affords a valid approach to improve the stability and mechanical robustness of OSCs, as well as ensuring the reproducibility of organic semiconductors during mass production.

Green Printing for Scalable Organic Photovoltaic Modules by Controlling the Gradient Marangoni Flow

Despite the rapid development in the performances of organic solar cells (OSCs), high-performance OSC modules based on green printing are still limited. The severe Coffee-ring effect (CRE) is considered to be the primary reason for the nonuniform distribution of active layer films. To solve this key printing problem, the cosolvent strategy is presented to deposit the active layer films. The guest solvent Mesitylene with a higher boiling point and a lower surface tension is incorporated into the host solvent o-XY to optimize the rheological properties, such as surface tension and viscosity of the active layer solutions. And the synergistic effect of inward Marangoni flow generation and solution thickening caused by the cosolvent strategy can effectively restrain CRE, resulting in highly homogeneous large-area active layer films. In addition, the optimized crystallization and phase separation of active layer films effectively accelerate the charge transport and exciton dissociation of devices. Consequently, based on PM6:BTP-eC9 system, the device prepared with the co-solvent strategy shows the a power conversion efficiency of 17.80%. Moreover, as the effective area scales to 1 and 16.94 cm2, the recorded performances are altered to 16.71% and 14.58%. This study provides a universal pathway for the development of green-printed high-efficiency organic photovoltaics.

Polymer-Entangled Spontaneous Pseudo-Planar Heterojunction for Constructing Efficient Flexible Organic Solar Cells

Flexible organic solar cells (FOSCs) have attracted considerable attention from researchers as promising portable power sources for wearable electronic devices. However, insufficient power conversion efficiency (PCE), intrinsic stretchability, and mechanical stability of FOSCs remain severe obstacles to their application. Herein, an entangled strategy is proposed for the synergistic optimization of PCE and mechanical properties of FOSCs through green sequential printing combined with polymer-induced spontaneous gradient heterojunction phase separation morphology. Impressively, the toughened-pseudo-planar heterojunction (Toughened-PPHJ) film exhibits excellent tensile properties with a crack onset strain (COS) of 11.0%, twice that of the reference bulk heterojunction (BHJ) film (5.5%), which is among the highest values reported for the state-of-the-art polymer/small molecule-based systems. Finite element simulation of stress distribution during film bending confirms that Toughened-PPHJ film can release residual stress well. Therefore, this optimal device shows a high PCE (18.16%) with enhanced (short-circuit current density) JSC and suppressed energy loss, which is a significant improvement over the conventional BHJ device (16.99%). Finally, the 1 cm2 flexible Toughened-PPHJ device retains more than 92% of its initial PCE (13.3%) after 1000 bending cycles. This work provides a feasible guiding idea for future flexible portable power supplies.

Achieving Desired Pseudo-Planar Heterojunction Organic Solar Cells via Binary-Dilution Strategy

The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo-planar heterojunction (P-PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary-dilution strategy is proposed, the PM6 solution with micro acceptor BO-4Cl and the L8-BO solution with micro donor PM6 respectively, to form P-PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO-4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P-PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short-circuit current density of 26.92 mA cm-2 , much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high-performance OSCs.

Suppressed Ion Migration in FA-Rich Perovskite Photovoltaics through Enhanced Nucleation of Encapsulation Interface

With excellent homogeneity, compactness and controllable thickness, atomic layer deposition (ALD) technology is widely used in perovskite solar cells (PSCs). However, residual organic sources and undesired reactions pose serious challenges to device performance as well as stability. Here, ester groups of poly(ethylene-co-vinyl acetate) are introduced as a reaction medium to promote the nucleation and complete conversion of tetrakis(dimethylamino)tin(IV) (TDMA-Sn). Through simulations and experiments, it is verified that ester groups as Lewis bases can coordinate with TDMA-Sn to facilitate homogeneous deposition of ALD-SnOx , which acts as self-encapsulated interface with blocking properties against external moisture as well as internal ion migration. Meanwhile, a comprehensive evaluation of the self-encapsulated interface reveals that the energy level alignment is optimized to improve the carrier transport. Finally, the self-encapsulated device obtains a champion photovoltaic conversion efficiency (PCE) of 22.06% and retains 85% of the initial PCE after being stored at 85 °C with relative humidity of 85% for more than 800 h.

Delayed Crystallization Kinetics Allowing High-Efficiency All-Polymer Photovoltaics with Superior Upscaled Manufacturing

Though encouraging performance is achieved in small-area organic photovoltaics (OPVs), reducing efficiency loss when evoluted to large-area modules is an important but unsolved issue. Considering that polymer materials show benefits in film-forming processability and mechanical robustness, a high-efficiency all-polymer OPV module is demonstrated in this work. First, a ternary blend consisting of two polymer donors, PM6 and PBQx-TCl, and one polymer acceptor, PY-IT, is developed, with which triplet state recombination is suppressed for a reduced energy loss, thus allowing a higher voltage; and donor-acceptor miscibility is compromised for enhanced charge transport, thus resulting in improved photocurrent and fill factor; all these contribute to a champion efficiency of 19% for all-polymer OPVs. Second, the delayed crystallization kinetics from solution to film solidification is achieved that gives a longer operation time window for optimized blend morphology in large-area module, thus relieving the loss of fill factor and allowing a record efficiency of 16.26% on an upscaled module with an area of 19.3 cm2 . Besides, this all-polymer system also shows excellent mechanical stability. This work demonstrates that all-polymer ternary systems are capable of solving the upscaled manufacturing issue, thereby enabling high-efficiency OPV modules.

Impact of Electrostatic Interaction on Non-radiative Recombination Energy Losses in Organic Solar Cells Based on Asymmetric Acceptors

Reducing non-radiative recombination energy loss (ΔE3 ) is one key to boosting the efficiency of organic solar cells. Although the recent studies have indicated that the Y-series asymmetric acceptors-based devices featured relatively low ΔE3 , the understanding of the energy loss mechanism derived from molecular structure change is still lagging behind. Herein, two asymmetric acceptors named BTP-Cl and BTP-2Cl with different terminals were synthesized to make a clear comparative study with the symmetric acceptor BTP-0Cl. Our results suggest that asymmetric acceptors exhibit a larger difference of electrostatic potential (ESP) in terminals and semi-molecular dipole moment, which contributes to form a stronger π-π interaction. Besides, the experimental and theoretical studies reveal that a lower ESP-induced intermolecular interaction can reduce the distribution of PM6 near the interface to enhance the built-in potential and decrease the charge transfer state ratio for asymmetric acceptors. Therefore, the devices achieve a higher exciton dissociation efficiency and lower ΔE3 . This work establishes a structure-performance relationship and provides a new perspective to understand the state-of-the-art asymmetric acceptors.

Self-encapsulated wearable perovskite photovoltaics via lamination process and its biomedical application

Flexible perovskite solar cells (PSCs) are highly promising photovoltaic technologies due to the prospect of integration with wearable devices. However, conventional encapsulation strategies for flexible devices often cause secondary damage to the perovskite crystals, which affects device performance. Here, we present self-encapsulated flexible PSCs realized by lamination technology. The conversion of perovskite crystals is achieved by the diffusion of lead iodide and ammonium halide under the effect of temperature and pressure. In addition, the hydrogen bonding of the introduced polyacrylamide enhances the connections of the integral device while improving the crystal quality. The self-encapsulated flexible PSCs achieve an outstanding photovoltaic conversion efficiency of 22.33%, and comprehensive stability tests are conducted based on wearable device application scenarios to verify the feasibility. Finally, 25 cm² wearable perovskite modules are successfully applied into the neuro-assisted wearable devices.

The solvent effect on the morphology and molecular ordering of benzothiadiazole-based small molecule for inkjet-printed thin-film transistors

A small molecule organic semiconductor, D(D'-A-D')₂ comprising benzothiadiazole as an acceptor, 3-hexylthiophene, and thiophene as donors, was successfully synthesized. X-ray diffraction and atomic force microscopy were used to investigate the effect of a dual solvent system with varying ratios of chloroform and toluene on film crystallinity and film morphology via inkjet printing. The film prepared with a chloroform to toluene ratio of 1.5 : 1 showed better performance with improved crystallinity and morphology due to having enough time to control the arrangement of molecules. In addition, by optimizing ratios of CHCl₃ to toluene, the inkjet-printed TFT based on 3HTBTT using a CHCl₃ and toluene ratio of 1.5 : 1 was successfully fabricated and exhibited a hole mobility of 0.01 cm² V^-1 s^-1 due to the improved molecular ordering of the 3HTBTT film.

Ionic Liquid Assisted Imprint for Efficient and Stable Quasi-2D Perovskite Solar Cells with Controlled Phase Distribution

Although two-dimensional perovskite devices are highly stable, they also lead to a number of challenges. For instance, the introduction of large organic amines makes crystallization process complicated, causing problems such as generally small grain size and blocked charge transfer. In this work, imprint assisted with methylamine acetate were used to improve the morphology of the film, optimize the internal phase distribution, and enhance the charge transfer of the perovskite film. Specifically, imprint promoted the dispersion of spacer cations in the recrystallization process with the assistance of methylamine acetate, thus inhibited the formation of low-n phase induced by the aggregation of spacer cations and facilitated the formation of 3D-like phase. In this case, the corresponding quasi-2D perovskite solar cells delivered improved efficiency and exhibited superior stability. Our work provides an effective strategy to obtain uniform phase distribution for quasi-2D perovskite.