Chen Weijie

Herein, a 2,7-dibromo-9,9-dimethylfluorene (DBDMF)-based solid additive with a low volatile and high crystalline nature is introduced in the active layer of organic solar cells. The influence of DBDMF on the film morphologies, optical properties, and photovoltaic performences is comprehensively studied.

Organic solar cells (OSCs) have drawn lots of attention because of their rapid development and great potential in large-area flexible electronics. Recently, volatile solid additives have been widely used in optimizing morphologies of active layers and improving device performances for nonfullerene (NF)-based OSCs. Most solid additives, however, still suffer severe problems such as unsuitable volatile temperatures and requirement of extra solvent additives. Herein, a new solid additive 2,7-dibromo-9,9-dimethylfluorene (DBDMF) with a high crystallinity and suitable volatile temperature as an additive for NF-based OSCs is designed. DBDMF can suppress the overaggregation of the nonfullerene acceptors (NFAs) and improve the material rearrangements after thermal annealing because of the good miscibility with the NFAs. As a result, DBDMF-treated OSC devices display more favorable film morphologies and phase separation, well-balanced charge mobilities, higher electron transfer rates, and better device stability. Consequently, the PM6:BTP-BO-4F binary system shows an outstanding power conversion efficiency of 17.2% from 15.3% with a simultaneous increase in the fill factor from 71.4 to 77.1%. Furthermore, DBDMF has been applied to other two active layers, manifesting the general applicability. This study demonstrates a feasible and promising approach to develop volatilizable solid additives for improving performance and stability of NF-based OSCs.

Solvent-induced polymorphism is revealed for chloroform (CF) and chlorobenzene (CB)-processed 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophne) (ITIC). Due to the different interaction between solvent and ITIC, the CB-induced phase shows ordered lamellar and π–π stacking. CF-processed ITIC polymorph leads to higher crystallization and melting temperatures. The polymorphism results in distinct differences on the performance and thermal stability of organic solar cells.

Organic photovoltaics have achieved breakthroughs in power conversion efficiency due to the superior aggregation and packing nature of non-fullerene acceptors (NFAs). Solution processing and various treatments would tend to form distinct packing motifs for state-of-the-art NFAs. Herein, the solvent-induced polymorphism for 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophne) (ITIC) prepared by chloroform (CF) and chlorobenzene (CB) is revealed. The packing motif of ITIC exhibits dense π–π stacking from CF induction, which presents red-shifted absorption and reversible high-temperature crystallization and melting. Meanwhile, strong lamellar stacking and π–π stacking can be formed in the CB solution with unstable low-temperature crystallization and melting. Combining in situ absorption spectra and interaction calculation, the stronger preaggregation of ITIC in the CF solution was found to be the main reason for forming a different packing motif from in the CB solution. The packing and thermodynamic features are retained in the PBDB-T:ITIC blends, though good miscibility weakens characteristic features. Benefiting from the polymorph structure, CB-processed devices denote more favorable performance but less thermal stability. This research indicates the significant effect of solvent induction for manipulating and optimizing the morphology of organic solar cell devices.

Substoichiometric tungsten oxide (WO_3−X ) nanorods with adjustable localized surface plasmon resonance effect are introduced into perovskite via the antisolvent method to expand light absorption range of perovskite solar cells (PSCs), increase the carrier concentration in the perovskite layer, and accelerate charge transfer through near-field enhancement. The highest power conversion efficiency of 21.14% has been achieved in MAPbI₃-based PSCs.

The collaborative strategy of optical design and charge transport dynamics optimization can provide double guarantee to achieve high-efficient planar perovskite solar cells (PSCs). Herein, WO_3−X nanorods with tunable localized surface plasmon resonance (LSPR) effect are introduced at the interface between perovskite and hole transport layer (HTL) via antisolvent method during the preparation of perovskite films. The photocurrent of WO_3−X nanorods-based devices significantly increases due to the extension of absorption region caused by LSPR effect. The charge transfer at the perovskite/HTL interface is also accelerated due to the electromagnetic near-field enhancement via the LSPR effect. The synchronized improvement in photocurrent and charge transfer by WO_3−X nanorods leads to a power conversion efficiency of 21.14% in MAPbI₃-based PSCs. This work not only provides an effective approach to enhance the photovoltaic performance of PSCs, but also demonstrates the potential application of inorganic oxide semiconductors with LSPR in other optoelectronic devices.

By employing 4,4'-sulfonyldiphenol (DSP) to passivate the perovskite surface, the intrinsic defect density is successfully modified and the oxidation of Sn²⁺ is suppressed. Furthermore, the resulting energy-level alignment significantly promotes the champion power conversion efficiency (PCE) of the hole transport layer-free Sn–Pb mixed narrow bandgap (E _g = 1.26 eV) perovskite solar cells to 21.43% with a V _oc of 0.876 V.

There have been a number of remarkable signs of progress achieved in tin–lead mixed narrow-bandgap perovskite solar cells (PSCs) due to the high theoretical power conversion efficiency (PCE) and their promising application in tandem devices. Indeed, Sn–Pb mixed PSCs without a hole transport layer (HTL) also have been more attractive owing to lower cost and simplification of the device structure. However, the defects in perovskite film introduced by Sn²⁺ oxidation severely restrict device efficiency and stability.Herein, a small organic molecule, 4,4'-sulfonyldiphenol, is employed to passivate perovskite (E _g = 1.26 eV) surface to decrease the interfacial defects and suppress the nonradiative carrier recombination. Furthermore, by regulating energy-level alignment, charge carrier extraction is greatly facilitated. The device performance is significantly enhanced in that the champion PCE is enlarged to 21.43% with an open-circuit voltage (V _oc) of 0.876 V from only 18.02% with a V _oc of 0.770 V. The stability of unencapsulated devices is improved substantially as well while retaining 80% PCE of its initial value after being stored in the glovebox for around 600 h. This facile but highly effective strategy successfully proposes the promising development of HTL-free Sn–Pb mixed PSCs.

The efficiency of the perovskite solar cell (PSC) is developing rapidly while its poor stability is still the fatal defect. Atomic layer deposition (ALD) provides some solutions for it. Herein, some typical cases reported in recent years for preparing PSCs buffer and encapsulation layers using ALD technology to improve device stability are reviewed.

Organic–inorganic mixed perovskite solar cells (PSCs) have been rapidly developed. However, while efficiency is improved, stability is still a problem that hinders further commercial production. Researchers have adopted many solutions and technological means to solve this problem, such as additive engineering, interface engineering, encapsulation engineering, and so on. To achieve the goal, various technical means have been employed. Among them, atomic layer deposition (ALD) is an effective tool to prepare compact pinhole-free thin films at low temperature, and its introduction provides some solutions to improve the stability of devices. Herein, the typical cases reported in recent years of preparing PSCs buffer and encapsulation layers using ALD technology to improve device stability are reported. The specific role of ALD in this process is analyzed, and the prospects and challenges of its further application are also discussed prospectively.

A bathocuproine (BCP):silver buffer layer is introduced to modulate the tunneling junction contact for perovksite/TOPCon tandem solar cell. Owing to reduced sputter damages and enhanced carrier transport, the optimized tandem device achieves a champion power conversion efficiency of 25.84% (certified).

The single-crystalline silicon solar cell with tunnel oxide passivating poly-Si contact (TOPCon) has developed into one of the most promising and high-performance n-type Si-based solar cells in their mass production way because of its high conversion efficiency and robustness. Owing to its unique device structure, TOPCon shows superior advantages over amorphous Si-based heterojunction one (HJT) in developing high-performance monolithic perovskite/silicon tandem solar cell because TOPCon may have better tolerance than HJT to the particle bombardments and plasma fluorescence irradiations in the sputtering deposition process of transparent conductive oxide (TCO) recombination layer. Herein, bathocuproine (BCP):silver complex is introduced as a buffer recombination contact between TCO and poly-SiC_X, to modulate the tunneling junction between perovskite/TOPCon. Depending on fine film thickness and derived energy level tuning, BCP:Ag buffer layer can effectively prevent the sputter bombardments and passivate the interface of TCO/poly-SiC_X(n)/SiO_X contact, as well as enhancing electron transport. As a result, a certified conversion efficiency of 25.84% is achieved in the monolithic perovskite/TOPCon silicon tandem solar cell. This work definitely paves a new and promising way to develop high-performance monolithic perovskite/c-Si tandem solar cells.

Accurate measurement of the power conversion efficiencies of perovskite-containing multijunction solar cells is more complicated than for a single-junction cell. Measurement conditions for accurate performance testing of perovskite-containing multijunctions, including perovskite-Si and all-perovskite tandems are discussed. Common errors and pitfalls that sometimes mislead the interpretation of the results and recommendations for evaluating the accuracy of the data are presented.

Perovskite multijunctions (PVSK MJs) have made remarkable progress with monolithic PVSK/PVSK tandems surpassing the efficiency of single-junction (1 J) PVSK cells and PVSK/Si cells reported to exceed the 30% efficiency mark. These efficiencies are reported at standard test conditions (STC), established by the photovoltaic (PV) community to facilitate comparison between devices and technologies. Herein, it is discussed why an accurate STC performance measurement for a MJ is more complicated than for a 1 J cell and the special aspects to be considered when measuring the current–voltage characteristics and the performance of PVSK-containing MJ cells are emphasized. It is discussed why a spectrally adjustable solar simulator is needed and the sequence of accurate performance measurement, namely measurement of the spectral response of each junction, adjustment of the spectrum, and appropriate protocols for measuring the power output of the device at STC, is presented. For all these, common errors and pitfalls that sometime lead to misleading interpretation of the results are presented, and the methods to evaluate the accuracy of the data when a spectrally adjustable solar simulator is not available are recommended. Finally, first step is taken toward recommending performance measurement approaches when high throughput is required as will eventually be in a production line.

1-Ethyl-3-methylimidazolium acetate ionic liquid is introduced to decrease deep-level defects induced by surface undercoordinated Sn²⁺ in CsSnI₃ perovskites through strong electrostatic attraction and coordination interaction. The optimized mesoporous device exhibits a power conversion efficiency of 8.54%, which is the champion among all the reported CsSnI₃ mesoporous perovskite solar cells to now.

Inorganic tin halide perovskite compound with its eco-friendly property has attracted tremendous attention of researchers in the field of lead-free perovskite solar cells. However, the trap-assisted nonradiative recombination caused by deep-level defects originating from surface undercoordinated Sn²⁺ cations significantly deteriorates the CsSnI₃ device's performance. Herein, adding low concentrations of an ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc) shows promise in controlling deep-level defects in CsSnI₃ perovskites. Both experimental observation and theoretical simulation reveal that EMIMAc can have strong electrostatic attraction and coordination interaction with the surface undercoordinated Sn²⁺ through the lone electron pairs of carboxyl functional groups and the donated π electrons from electron-rich imidazole moieties, leading to a reduced deep-level defect density and a restrained nonradiative recombination. Consequently, the processed CsSnI₃ perovskite solar cells based on a printable fluorine-doped tin oxide/compact-TiO₂/mesoporous-TiO₂/Al₂O₃/NiO/carbon framework achieve a power conversion efficiency as high as 8.54%, which is the champion efficiency among all the reported CsSnI₃ mesoporous perovskite solar cells up to now. In addition, the unencapsulated devices have shown an impressive long-term stability with only ≈6% efficiency degradation after over 2000 h aging under nitrogen atmosphere.

Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO₂/FA_0.83Cs_0.17PbI₃. Comprehensive characteristics reveal that PSiOH can reduce surface defects, improve electrical properties and optimize energy band structure of TiO₂, and passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified perovskite solar cells (PSCs) yield a remarkable efficiency of 24.20% and improved stability.

Abstract

Suppressing defects at the interface between the TiO₂ electron transport layer (ETL) and perovskite film is critical for high efficiency and stable perovskite solar cells (PSCs). Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO₂ ETL/FA_0.83Cs_0.17PbI₃ perovskite. Comprehensive characteristics reveal that silicon hydroxyl (SiOH) in PSiOH can reduce surface defects, improve the electrical properties and optimize the energy band structure of TiO₂ by forming a SiOTi bond, while the phosphate bond (PO) in PSiOH can passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified PSCs yield a remarkable power conversation efficiency of 24.20% and improved air, thermal, or illumination stabilities. This study provides insight into passivation defects at the buried interface for efficient and stable PSCs.

Medium bandgap isomeric small molecule acceptors m-DTC-Cl-1 and m-DTC-Cl-2 with different chlorine substitution positions is designed and synthesized. The devices based on m-DTC-Cl-2 show better charge dynamics and film morphology. The monolithic tandem organic solar cell based on PTO2:m-DTC-Cl-2 as the front cell demonstrates a high efficiency of 18.8%.

Abstract

Tandem organic solar cell (TOSC), composed of the front and rear cells with complementary absorption, is effective device structure for surpassing the Shockley–Queisser limit of single-junction organic solar cells (OSCs). However, most of the medium bandgap (≈1.6 eV) organic photovoltaic materials for front cells in the TOSCs show considerable voltage losses. In this work, two medium bandgap (1.63 eV) isomeric small molecule acceptors m-DTC-Cl-1 and m-DTC-Cl-2 are synthesized with different chlorine substitution positions in 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC). The different chlorine substituted positions in IC groups show significant influences on the physicochemical properties, charge dynamics, morphology, and photovoltaic performance of the acceptors. Consequently, the OSC with PTO2 as polymer donor and m-DTC-Cl-2 as acceptor delivers a champion power conversion efficiency (PCE) of 14.1% with a high open circuit voltage of 1.05 V and a low nonradiative energy loss of 0.25 eV, which indicates that the OSC is an ideal candidate for the application as front cell in the TOSCs. Then, a monolithic TOSC is fabricated with the OSC based on PTO2:m-DTC-Cl-2 as front cell and the OSC based on PTB7-Th:BTPV-4Cl as rear cell, which demonstrates a high PCE of 18.8%.

Two small-molecule donors, namely T4 and T6, with different substituents on their selenophene conjugated units are developed, of which T4 with alkyland T6 with trialkylsilyl. The all-small-molecule organic solar cell based on T6:N3 yields a power conversion efficiency (PCE) as high as 16.03%, significantly higher than that based on T4:N3 (PCE = 12.61%).

Abstract

Fibrous interpenetrating network structure morphology is extremely crucial for all-small-molecule organic solar cells (ASM-OSCs) in achieving high power conversion efficiency (PCE). Rational molecular design and suitable posttreatment to the film are feasible methods to accomplish this goal. Herein, two small molecule donors, namely T4 and T6, with different substituents on their selenophene conjugated units, alkyl for T4 while trialkylsilyl for T6, are developed. Both as cast devices obtain poor PCEs (≈4.5%) when blending these two donors with N3 due to the oversize phase separation. Satisfactorily, the PCEs are dramatically increased after CS₂ annealing, which mainly originates from the favorable reorganization of donor and acceptor in the active layer, ultimately improving the phase separation and vertical electronic properties. As a result, the device based on trialkylsilyl-substituted T6 acquires a remarkable PCE of 16.03%, much higher than that of the blends of alkyl-substituted T4 and N3 (12.61%). The enhanced PCE of the T6-based device is attributed to the deeper HOMO energy levels, more obvious fibrous interpenetrating networks, and stronger molecular interaction between T6 and N3, as compared with T4-based ones. This study indicates that precise molecular design and the proper posttreatment process can be a brilliant approach for realizing highly efficient ASM-OSCs.

Perovskite solar cells (PSCs) have made unprecedented progress in the past decade. However, potential lead leakage from PSCs is becoming a key issue restricting their deep development for commercialization. In this review, first, the toxicity of lead and the impact of lead ions from halide perovskites, and the effort to develop lead-free perovskites are discussed. Then, the recent progress made to reduce the leakage of lead ions from damaged PSC modules is introduced. Subsequently, a concise overview of the recyclability of damaged or decommissioned PSC devices is discussed. Finally, the insights into current challenges and future directions in this emerging area of research are presented.

Abstract

Perovskite solar cells (PSCs) have made unprecedented progress in improving power conversion efficiency in the past decade, and they are considered as one of the most promising photovoltaic technologies. However, the commercialization of PSCs still faces significant challenges, such as the stability issue and toxicity of lead. Recently, pursuing ways to alleviate the toxicity of lead has emerged as an attractive research direction in the community of PSCs. In this review, the discussion is on the toxicity of lead and the impact of lead leakage from perovskites to the environment, the recent progress made to reduce the leakage of lead is presented with an emphasis on the lead sequestration materials applied in encapsulation layers and functional layers of PSCs, and the recovery of lead from damaged or decommissioned PSC devices is concisely summarized. This review may serve as a guide for researchers interested in promoting PSCs from exploitation to application.

A molecular bridge strategy is developed to modify the buried interfaces in n–i–p perovskite solar cells. The treatment enables bifacial defects passivation and improved perovskite quality, enhancing electron extraction and suppressing non-radiative recombination at the buried interfaces. Improved efficiency of up to 23.07% and 21.50% is realized in rigid and flexible devices. Besides, the corresponding devices with encapsulation demonstrate superior stability under different conditions.

Abstract

Interface engineering is of paramount importance for optimizing carrier dynamics and stability of perovskite solar cells (PSCs), but little attention has been paid to understanding and managing the buried interfaces. Here, a molecular bridge strategy is developed to modify the properties of buried interfaces in n–i–p PSCs by introducing a multi-functional additive 2-Hydroxyethyl trimethylammonium chloride (ChCl) in the bottom SnO₂ electron transport layer. The ChCl treatment enables bifacial defects passivation and improved perovskite quality, leading to notably enhanced electron extraction and suppressed non-radiative recombination at the buried interfaces. As a result, a significantly improved power conversion efficiency (PCE) from 20.0% to 23.07% with a remarkable open-circuit voltage (V _oc) of up to 1.193 V is achieved, along with superior stability (up to 4000 h) for the unsealed devices under different conditions (moisture, heat and maximum power point). Furthermore, this molecular bridge strategy demonstrates the ability to release the stress in perovskite thin film and simultaneously strengthen the interfacial toughness in flexible PSCs, yielding remarkable mechanical stability and a champion PCE of 21.50%. This study offers deep insights into understanding and engineering the buried interfaces and provides effective strategies to further enhance the performance and stability of PSCs.

Publication date: 21 December 2022

Source: Joule, Volume 6, Issue 12

Author(s): Haibing Wang, Feihong Ye, Jiwei Liang, Yongjie Liu, Xuzhi Hu, Shun Zhou, Cong Chen, Weijun Ke, Chen Tao, Guojia Fang

Publication date: 15 December 2022

Source: Nano Energy, Volume 104, Part A

Author(s): Jingwei Zhu, Benlin He, Mengxin Wang, Xinpeng Yao, Hao Huang, Cong Chen, Haiyan Chen, Yanyan Duan, Qunwei Tang

Publication date: 15 December 2022

Source: Nano Energy, Volume 104, Part A

Author(s): Tao Zhang, Qingquan He, Jiewen Yu, An Chen, Zenan Zhang, Jun Pan

A dual-metal doping defect engineering strategy is developed to minimize non-radiative recombination, mitigate hysteresis, improve efficiency with low voltage deficit and extended lifespan in perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) have witnessed an unprecedentedly rapid development, especially in terms of power conversion efficiency (PCE). However, the solution-processed perovskite films inevitably possess numerous crystallographic defects (e.g., halide vacancies), which has been shown to incur non-radiative charge recombination and ion migration, thus limiting the enhancement of the PCE and stability of PSCs. Here, a novel dual metal (i.e., divalent and monovalent metal ions) modification strategy is reported for simultaneously reducing the defects, immobilizing the halide anions, and preventing ion loss from perovskite during post-annealing process. Accordingly, this strategy significantly reduces non-radiative recombination, enhancing the PCE by ≈12% and mitigating the current density-voltage (J–V) hysteresis effect in resultant devices compared to undoped counterparts. As a result, a champion PCE exceeding 22% and a high open-circuit voltage (V_oc ) of 1.16 V is obtained for dual metal ions-modified PSCs. The optimized devices also exhibit extended lifespan upon the dual metal treatment. The study provides a new defect engineering strategy toward more efficient and stable perovskite photovoltaics.

The crystallinity and quantum well orientation of formamidinium based low-n 2D perovskite are fine-tuned by ionic additives of NH₄ ⁺ and SCN⁻. The present strategy can significantly retard the heterogeneous crystallization of low-n phases in the intermediate state, driving the templated vertical growth of quantum well structures. An air stable perovskite solar cell with record power conversion efficiency of 18.14% is achieved.

Abstract

The relatively lower crystallinity and random orientation of quantum well structures hinder carrier transport and limit the performance of formamidinium (FA) based low-n 2D perovskite devices. In this work, the crystallization and quantum well orientation are fine tuned to achieve efficient low-n FA based Ruddlesden–Popper perovskite solar cells. The effects of different ionic additives on the crystallization, orientation, and photovoltaic performance of FA based low-n 2D perovskites are comparatively investigated. It is found that NH₄ ⁺ and SCN⁻ can significantly retard the heterogeneous crystallization of low-n phases in the intermediate state, and drive the templated growth of quantum well structure with vertical orientation. The optimized photovoltaic device based on (BA)₂(FA)₃Pb₄I₁₃ achieved a power conversion efficiency (PCE) of 18.14%, setting the highest record for FA-based low-n 2D perovskite solar cells as far as it is known (average n = 4). The unencapsulated device exhibited excellent stability and maintained 93.3% of its original PCE at 85 °C, and 86.3% at 1 Sun illumination after 720 h in humid ambient condition.

MPhS-C2 with shortened terminal alkyl chain, features thermal annealing (TA)-insensitive aggregation and condense packing, leading to suppressed upshifts of highest occupied molecular orbital energy level during TA, and efficient charge transport at small phase separation in BTP-eC9 blended devices, obtaining the highest PCE of 17.11% with ΔV _nr of 0.192 V in ASM-OSCs.

Abstract

A critical bottleneck for further efficiency breakthroughs in organic solar cells (OSCs) is to minimize the non-radiative energy loss (eΔV _nr) while maximizing the charge generation. With the development of highly emissive low-bandgap non-fullerene acceptors, the design of high-performance donors becomes critical to enable the blend with the electroluminescence quantum efficiency to approach or surpass the pristine acceptor. Herein, by shortening the end-capped alkyl chains of the small-molecular donors from hexyl (MPhS-C6) to ethyl (MPhS-C2), the material obtained aggregation that was insensitive to thermal annealing (TA) along with condensed packing simultaneously. The former leads to small phase separation and suppressed upshifts of the highest occupied molecular orbital energy level during TA, and the latter facilitates its efficient charge-transport at aggregation-less packing. Hence, the ΔV _nr decreases from 0.242 to 0.182 V, from MPhS-C6 to MPhS-C2 based OSCs. An excellent PCE of 17.11% is obtained by 1,8-diiodoctane addition due to almost unchanged high J _sc (26.6 mA cm⁻²) and V _oc (0.888 V) with improved fill factor, which is the record efficiency with the smallest energy loss (0.497 eV) and ΔV _nr (0.192 V) in all-small-molecule OSCs. These results emphasize the potential material design direction of obtaining concurrent TA-insensitive aggregation and condensed packing to maximize the device performances with a super low ΔV _nr.

Liquid-crystal (LC) molecules interacting with PbI₂ retard the crystallization of the perovskite film, and finally increase the grain size. During annealing, the LC molecules undergo a phase transition, and then the flowable LC is extracted by the lower interface to release the residual stress, and accelerate electron extraction. A new engineering of additive phase transition is thus conceived.

Abstract

Low-temperature solution processing of thin-film semiconductors is more cost-effective than traditional vacuum processing; however, it leads to more defects during fast bulk crystallization and residual tensile stress. Herein, a new strategy of dynamic liquid-crystal transition (DLCT) is developed to solve these problems in one step. The design principle is used to suggest that the DLCT molecule should firstly interact with the perovskite grains in the bulk and meanwhile go through a dynamic transition to spontaneously heal the interface. A thermotropic LC molecule (CBO6SS6OCB) is then designed to demonstrate the strategy. The LC interacting with perovskite colloid forms an intermediate adduct to retard the crystallization. The annealing processes stimulate the concentrated LC solid, causing it to flow to the electron transport layer to release the residual stress to attain improved electron extraction. Consequently, the device efficiency is increased to 24.38%, where its V _OC of 1.184 V is among the best for the formamidine-based perovskite solar cells. Furthermore, the ambient stability (93.0% of initial efficiency after 2000 h of aging) and light stability (96.3% of initial efficiency after 500 h of aging) are much improved. This work conceives a new engineering of additive phase transition for high-performance perovskite solar cells.

Regulation of the configurations of the non-conjugated polymer acceptors enables green solvent-processed large-area binary all-polymer solar cells to achieve record efficiency and robustness. This study not only provides a series of reliable novel conductive materials with excellent performance for flexible wearable solar cells but also elucidates a concept to evaluate the comprehensive performance of organic solar cells.

Abstract

With the great potential of the all-polymer solar cells for large-area wearable devices, both large-area device efficiency and mechanical flexibility are very critical but attract limited attention. In this work, from the perspective of the polymer configurations, two types of terpolymer acceptors PYTX-A and PYTX-B (X = Cl or H) are developed. The configuration difference caused by the replacement of non-conjugated units results in distinct photovoltaic performance and mechanical flexibility. Benefiting from a good match between the intrinsically slow film-forming of the active materials and the technically slow film-forming of the blade-coating process, the toluene-processed large-area (1.21 cm²) binary device achieves a record efficiency of 14.70%. More importantly, a new parameter of efficiency stretchability factor (ESF) is proposed for the first time to comprehensively evaluate the overall device performance. PM6:PYTCl-A and PM6:PYTCl-B yield significantly higher ESF than PM6:PY-IT. Further blending with non-conjugated polymer donor PM6-A, the best ESF of 3.12% is achieved for PM6-A:PYTCl-A, which is among the highest comprehensive performances.