Chen Weijie

An indium-doped zinc oxide (IZO) electron transport layer (ETL) is developed for high-efficiency inverted organic solar cells, and indium doping can improve electron extraction and suppress charge recombination. A 1.2-micrometer-thick ultrathin flexible OSC achieves an efficiency of 17.0% with a power-per-weight ratio of 40.4 W g⁻¹, which is one of the highest values among ultrathin flexible organic solar cells.

Abstract

Sol–gel processed zinc oxide (ZnO) is one of the most widely used electron transport layers (ETLs) in inverted organic solar cells (OSCs). The high annealing temperature (≈200 °C) required for sintering to ensure a high electron mobility however results in severe damage to flexible substrates. Thus, flexible organic solar cells based on sol–gel processed ZnO exhibit significantly lower efficiency than rigid devices. In this paper, an indium-doping approach is developed to improve the optoelectronic properties of ZnO layers and reduce the required annealing temperature. Inverted OSCs based on In-doped ZnO (IZO) exhibit a higher efficiency than those based on ZnO for a range of different active layer systems. For the PM6:L8-BO system, the efficiency increases from 17.0% for the pristine ZnO-based device to 17.8% for the IZO-based device. The IZO-based device with an active layer of PM6:L8-BO:BTP-eC9 exhibits an even higher efficiency of up to 18.1%. In addition, a 1.2-micrometer-thick inverted ultrathin flexible organic solar cell is fabricated based on the IZO ETL that achieves an efficiency of 17.0% with a power-per-weight ratio of 40.4 W g⁻¹, which is one of the highest efficiency for ultrathin (less than 10 micrometers) flexible organic solar cells.

Nature, Published online: 24 June 2024; doi:10.1038/s41586-024-07705-5

Nature Energy, Published online: 24 June 2024; doi:10.1038/s41560-024-01558-y

Phosphorylcholine chloride is employed as the interfacial modification layer material between SnO₂ and perovskite layer, in which Cl⁻ passivated the oxygen vacancy defects of the electron transport layer by chemical doping, and P═O and ─N(CH₃)₃ ⁺ passivated the uncoordinated Pb²⁺, I⁻ ion defects on the bottom surface of the perovskite film. Eventually, an efficient and stable perovskite solar cell is prepared.

Abstract

The electron transport layer (ETL), perovskite layer, hole transport layer, and electrode layer collectively constitute the perovskite solar cells (PSCs). Each of these layers plays a critical role in the performance of devices. However, there are mismatches in crystal structure and energy levels between ETL materials and the perovskite layer, resulting in numerous defects at their interface. In this study, multifunctional organic molecule called phosphorylcholine chloride is designed to modify the interface between SnO₂ and perovskite layer. This modification serves to both reduce oxygen vacancy defects in the SnO₂ and passivate defects in the perovskite layer. Consequently, the conductivity and electron mobility of SnO₂ are improved, and the higher-quality of perovskite film is obtained. Ultimately, the optimized PSC device achieves an impressive champion power conversion efficiency (PCE) of 24.34% with minimal hysteresis index. Even after 1200 h of ambient exposure at 25 °C and 25% relative humidity without encapsulation, the device maintains an impressive 91.44% of its initial efficiency. Additionally, a PCE of 22.38% is attained in flexible PSCs. This research will pave the way for the development of low interface defects, high stability as well as high PCE perovskite solar cells.

Here, a liquid crystal elastomer (LCE) with high thermal conductivity and low elastic modulus is used as a buried interlayer to obtain stress-less perovskite films. The optimized thin films are utilized in both rigid and flexible perovskite solar cells, resulting in efficiencies of 24.5% and 22.8%, respectively. And they exhibit robust mechanical stability.

Abstract

Flexible perovskite solar cells (FPSCs) have gained considerable attention for potential applications in portable and wearable electronics. However, the design principles governing FPSCs remain incompletely understood. In this study, two critical factors—thermal conductivity and elastic modulus—that significantly influence the thermal and mechanical stabilities of FPSCs are identified. Achieving stress-less conditions is crucial for enhancing the performance of FPSCs. To address this, a liquid crystal elastomer (LCE) is employed as a buffer interlayer to effectively mitigate residual thermal stress. This is achieved by improving the thermal conductivity of the electron transport layer from 0.76 to 1.07 W mK⁻¹ and softening the perovskite layer, reducing the Young's modulus from 50 to 42 GPa. The optimized thin films are utilized in both rigid and flexible PSCs, resulting in efficiencies of 24.5% and 22.8%, respectively. Remarkably, these devices demonstrated excellent thermal stability, with unpackaged LCE rigid PSCs retaining 85.6% of their initial efficiency after 504 h of aging at 85 °C. Moreover, robust mechanical stability in FPSCs is exhibited, with 88.4% of the original efficiency retained after 5400 bending cycles. This investigation elucidates the profound impact of thermal conductivity and Young's modulus on the efficiency and stability of flexible electronics.

A mixed-SAM strategy (Mx-SAM) is proposed to enhance the adsorption energy of SAMs on the ITO surface, facilitate the formation of dense and humidity-resistant hole-selective layer (HSL) on substrates, the wide-bandgap (1.68 eV) PSCs achieved a PCE of 22.63%, and the fabricated industrially-compatible P/S-TSCs through antisolvent-assisted crystallization strategies achieve a remarkable efficiency of 28.07%.

Abstract

The antisolvent-assisted spin-coating still lags behind the thermal evaporation method in fabricating perovskite films atop industrially textured silicon wafers in making monolithic perovskite/silicon solar cells (P/S-TSCs). The inhomogeneity of hole-selective self-assembled monolayers (SAMs) often arises from the insufficient bonding between hygroscopic phosphonic acid anchors and metal oxide. To address this, a mixed-SAM strategy (Mx-SAM) is proposed to enhance the adsorption energy of SAMs on the ITO surface, facilitate the formation of dense and humidity-resistant hole-selective layer (HSL) on substrates, and improve hole transport capabilities. With the aid of the Mx-SAM strategy, the optimized wide-bandgap PSCs achieved an impressive power conversion efficiency (PCE) of 22.63% with an exceptionally high fill factor (FF) of 86.67% using the 1.68 eV perovskite. Moreover, they exhibited enhanced stability under damp-heat conditions (ISOS-D-3, 85% RH, 85 °C) with a T₉₀ of 900 h for encapsulated PSCs, representing one of the best performances for wide-bandgap PSCs. When further extending the Mx-SAM strategy to making P/S-TSCs using silicon wafers from industry, a remarkable efficiency of 28.07% is reached while upholding outstanding reproducibility. This strategy holds significant promise for the feasibility of fabricating industrially-compatible P/S-TSCs.

In this study, a bimolecular crystallization modulation strategy by using guanidine thiocyanate and aminoacetamide hydrochloride together as additives to improve the film quality of methylammonium-free Sn–Pb perovskites, which allows to fabricate Sn–Pb perovskite solar cells and all-perovskite tandem cells with encouraging efficiencies of 22.14% and 27.41%, respectively.

Abstract

The elimination of methylammonium (MA) cation from mixed tin–lead (Sn–Pb) narrow-bandgap (NBG) perovskites is an effective approach to enhance the operational stability of all-perovskite tandem solar cells (TSCs). Unfortunately, the uncontrolled nucleation and crystallization processes of MA-free Sn–Pb perovskites usually lead to inferior film quality and device performance. Herein, a bimolecular crystallization modulation strategy is reported by using guanidine thiocyanate (GuaSCN) and aminoacetamide hydrochloride (AHC) together as additives to improve the film quality of MA-free Sn–Pb perovskites. It is demonstrated that the use of bimolecular additives can effectively improve the crystallinity, increase the grain size, and induce a preferred (100) orientation for the corresponding films, leading to high-quality absorber with considerably reduced defect density and suppressed non-radiative recombination. In addition, the bimolecular additives can reduce the self-p-doping hole concentration within the perovskite films and enhance the charge extraction at the perovskite/electron transport layer interface. The modified NBG perovskite solar cells deliver a power conversion efficiency (PCE) of 22.14%. Coupled with the wide-bandgap (WBG) subcell, the all-perovskite TSCs give a champion certified PCE of 27.15%, which is the highest certified PCE for MA-free all-perovskite TSCs. Encapsulated tandem devices maintain 90% of the initial PCE after 473 h operation.

The ─NH₂ group of BAMPy reacts with FA⁺ to occupy A site of perovskite crystal framework, enhancing binding energy of ambient moisture with perovskites and thus relieving moisture interference on perovskite crystallization and structural homogeneity. The targeted PSCs fabricated under full-air conditions deliver the efficiency of 24.11% with exceptional operational stability.

Abstract

The fabrication of perovskite solar cells (PSCs) under full-air conditions accelerates their scalable production and industrialization. However, ambient moisture interacts with perovskites during the film formation that disturbs their crystallization and triggers structural imperfections. Here, a formamidine (FA) active addition reaction (FAAR) strategy is devised to intercept the deleterious chemical coordination. The simultaneous incorporation of 2, 6-bis(aminomethyl)pyridine (BAMPy) molecule into tin oxide surface and perovskite bulk ameliorates the interface contact and film interior. It is found that the tail amino group from BAMPy selectively reacts with FA cation, occupying A site of perovskite crystals, increasing binding energy of perovskite with H₂O molecule even in a defective surface, thereby strengthening moisture tolerance. This strategy effectively modifies perovskite crystallization in ambient air, favors structural uniformity, and forms the compressive-strained films. The FAAR-modified PSC devices fabricated under full-air conditions deliver the highest efficiencies of 24.11% and 21.68% with aperture areas of 0.06 and 1 cm², respectively. The favorable moisture impediment property contributes to perovskite crystallization enhancement and structural uniformity, maintaining 90.8% of their initial performance for the encapsulated devices after 2400 h storage under accelerating damp-heat measurements (85 °C and 85% relative humidity).

The conventional metal salts dopants used for spiro-OMeTAD degrade environmental and operational stability of perovskite solar cells. The ionic salt dopant introduced in this study not just functioned as an effective dopant for oxidizing spiro-OMeTAD with enhanced environmental stability, but also formed a 1D passivation layer through an interfacial reaction with the underlying perovskite film surface, resulting in significantly enhanced environmental and operational stability of perovskite solar cells.

Abstract

The ionic salt dopants devised to replace lithium bis(trifluoromethane)sulfonimide (Li-TFSI) used to dope widely used spiro-OMeTAD hole transporting material in perovskite solar cells (PSCs) has been reported to effectively suppress undesired side effects caused by the Li-TFSI. Nevertheless, roles of cationic molecules and its potential interactions with underlying perovskite film surface is largely unexplored. Here, it is unraveled that ionic salts introduced into the spiro-OMeTAD layer can chemically interact with underlying perovskite to induce an interfacial reaction. Inspiring from such interaction, a strategy is proposed to benefit from the interfacial reaction between the cation used for the dopant and underlying perovskite film surface to passivate surface defects. A simple quaternary alkylammonium salt, tetramethylammonium bis(trifluoromethanesulfonyl)imide (TMA-TFSI) is strategically adopted to demonstrate proof-of-concept devices. The TMA-TFSI not just functioned as an effective dopant for oxidizing spiro-OMeTAD with enhanced environmental stability, but also formed a 1D passivation layer through an interfacial reaction with the underlying perovskite film surface. Consequently, operational and environmental stability of the PSC are significantly enhanced with improved power output. This work should provide an important insight into the design of effective ionic salt dopants for PSCs to simultaneously improve performance and operational stability.

The 2D-ACG strategy is developed to control the nucleation and crystallization of the α-FAPbI₃-rich perovskite films. This involves utilizing in situ generated and embedded 2D perovskite as a template, thereby inducing perovskite growth. Consequently, the PSCs based on this strategy achieved an impressive efficiency of 26.16% (certified at 25.84%) along with superior film and device stability.

Abstract

Enhancing stability while maintaining high efficiency is among the primary challenges in the commercialization of perovskite solar cells (PSCs). Here, a crystal growth technique assisted by in situ generated 2D perovskite phases has been developed to construct high-quality 2D/3D perovskite films. The in situ generated 2D perovskite serve as templates for regulating the nucleation and oriented crystal growth in the α-FAPbI₃-rich film. This led to a high film quality with much reduced trap density and an ultralong carrier lifetime. The obtained perovskite film shows excellent stability under extreme environment conditions (T = 200 °C, RH = 75 ± 5%). The corresponding PSC achieved an efficiency of 26.16% (certified 25.84%), along with excellent operational stability (T93 > 1300 h, T ≅ 50 °C) as well as outstanding high and low temperature cycle stability.

Publication date: September 2024

Source: Nano Energy, Volume 128, Part B

Author(s): Haoliang Wang, Liangliang Deng, Tianxiang Hu, Xin Zhang, Xiaoguo Li, Yanyan Wang, Yaxin Wang, Yiting Liu, Xiaofei Yue, Zejiao Shi, Chongyuan Li, Kai Liu, Momin Sailai, Zhenye Liang, Chen Tian, Jiao Wang, Jia Zhang, Anran Yu, Xiaolei Zhang, Hongliang Dong

Publication date: September 2024

Source: Nano Energy, Volume 128, Part B

Author(s): Wenxuan Wang, Yong Cui, Yue Yu, Jianqiu Wang, Chaoyi Wang, Hao Hou, Qian Kang, Hui Wang, Shiyan Chen, Shaoqing Zhang, Haiping Xia, Jianhui Hou

Nature Energy, Published online: 21 June 2024; doi:10.1038/s41560-024-01564-0

Publication date: 21 August 2024

Source: Joule, Volume 8, Issue 8

Author(s): Xining Chen, Fu Yang, Linhao Yuan, Shihao Huang, Hao Gu, Xiaoxiao Wu, Yunxiu Shen, Yujin Chen, Ning Li, Hans-Joachim Egelhaaf, Christoph J. Brabec, Rui Zhang, Feng Gao, Yaowen Li, Yongfang Li

A donor–acceptor type semiconductor (BTF14) based on fluoranthene imide is introduced as the interlayer in NiO_x-based inverted perovskite solar cell, which facilitates the hole extraction and transfer, reduces the defect density, and suppresses the formation of Ni^>3+ to stabilize the heterointerface. Thus, the devices based on BTF14 delivers an encouraging efficiency up to 24.20%, with enhanced long-term operational and thermal stability.

Abstract

NiO_x is one of the promising inorganic hole transporting materials in inverted perovskite solar cells (PSCs), however, its device efficiency and stability are still limited by the energy level mismatch, low intrinsic conductivity, high interface defect density, and complex active species. Herein, the use of an imide-based donor–acceptor type semiconductor (BTF14) as the interlayer between perovskite and NiO_x is proposed, which facilitates the hole extraction and transfer, reduces the defect density at interface and in perovskite film bulk, and further reduces the concentration of Ni^>3+ species to stabilize the heterointerface. As a result, the power conversion efficiency of inverted PSCs can be significantly boosted from 22.11% of NiO_x to 24.20% of NiO_x/BTF14. Moreover, NiO_x/BTF14 based devices also exhibit negligible hysteresis and excellent long-term stability, with over 77% of their initial efficiency remaining after continuous operation at 60 °C for 1000 h under 1 sun illumination.

Publication date: September 2024

Source: Nano Energy, Volume 128, Part A

Author(s): Dan Zhou, Yanyan Wang, Yubing Li, Liangjing Han, Fang Wang, Senmei Lan, Ruizhi Lv, Lin Hu, Jiaping Xie, Jianwei Quan, Xufang Yang, Zhentian Xu, Lie Chen

Publication date: September 2024

Source: Nano Energy, Volume 128, Part A

Author(s): Baoqi Wu, Youle Li, Kangzhe Liu, Seoyoung Kim, Xiyue Yuan, Langheng Pan, Xia Zhou, Shizeng Tian, Changduk Yang, Fei Huang, Yong Cao, Chunhui Duan

Four 2D-conjugated guest acceptors (X-QTP-4F) are developed by attaching different halogens into the 2D-structured dibenzo[f,h]quinoxaline core. Among X-QTP-4F, Cl-QTP-4F shows a higher absorption coefficient, optimized molecular packing, suitable cascade energy levels, and complementary absorption with PM6:L8-BO host. Thus, ternary devices achieved 19% efficiency, which is among the state-of-the-art devices with 2D-structured acceptors.

Abstract

Halogenation of Y-series small-molecule acceptors (Y-SMAs) is identified as an effective strategy to optimize photoelectric properties for achieving improved power-conversion-efficiencies (PCEs) in binary organic solar cells (OSCs). However, the effect of different halogenation in the 2D-structured large π-fused core of guest Y-SMAs on ternary OSCs has not yet been systematically studied. Herein, four 2D-conjugated Y-SMAs (X-QTP-4F, including halogen-free H-QTP-4F, chlorinated Cl-QTP-4F, brominated Br-QTP-4F, and iodinated I-QTP-4F) by attaching different halogens into 2D-conjugation extended dibenzo[f,h]quinoxaline core are developed. Among these X-QTP-4F, Cl-QTP-4F has a higher absorption coefficient, optimized molecular crystallinity and packing, suitable cascade energy levels, and complementary absorption with PM6:L8-BO host. Moreover, among ternary PM6:L8-BO:X-QTP-4F blends, PM6:L8-BO:Cl-QTP-4F obtains a more uniform and size-suitable fibrillary network morphology, improved molecular crystallinity and packing, as well as optimized vertical phase distribution, thus boosting charge generation, transport, extraction, and suppressing energy loss of OSCs. Consequently, the PM6:L8-BO:Cl-QTP-4F-based OSCs achieve a 19.0% efficiency, which is among the state-of-the-art OSCs based on 2D-conjugated Y-SMAs and superior to these devices based on PM6:L8-BO host (17.70%) and with guests of H-QTP-4F (18.23%), Br-QTP-4F (18.39%), and I-QTP-4F (17.62%). The work indicates that halogenation in 2D-structured dibenzo[f,h]quinoxaline core of Y-SMAs guests is a promising strategy to gain efficient ternary OSCs.

For perovskite based on a two-step method, N-methylpyrrolidone (NMP) is doped into the PbI₂ solution to obtain a stable and homogeneous PbI₂-NMP complex. The interaction between NMP and FAI made it a bridge to promote the reaction between PbI₂ and FAI, leading to (001)-oriented quasi-single-crystal perovskite films with carrier lifetime of 1.5 µs and grain size larger than 3 µm. Solar cells exhibit an efficiency of 24.1% with working stability of T₉₆ = 300 h.

Abstract

Controllable fabrication of formamidinium (FA)-based perovskite solar cells (PSCs) with both high efficiency and long-term stability is the key to their further commercialization. However, the diversity of PbI₂ complexes and perovskite compositions usually leads to light sensitive PbI₂ residues and phase impurities in the film, which can accelerate the device degradation. Here, the crystallization kinetics of FA-based perovskite films are studied and a bridging-solvent strategy is proposed to modulate the reaction kinetics between PbI₂ and ammonium salts by prohibiting the formation of undesired intermediates. N-methylpyrrolidone (NMP) solvent is introduced into the PbI₂ precursor solution to obtain stable and homogeneous PbI₂-NMP complex films. The strong interaction between NMP and formamidinium iodide (FAI) molecules promotes the conversion from PbI₂-NMP into (001)-oriented quasi-single-crystal perovskite films with negligible impurities, long carrier lifetime of 1.5 µs and a large grain size of 3 µm. The optimized PSCs exhibit a high power conversion efficiency of 24.1%, as well as superior shelf stability which maintains 95% initial efficiency after storage in air for 1200 h (T₉₅ = 1200 h), and operating stability with T₉₆ = 300 h under continuous working at the maximum power point. This work offers a simple and reproducible method for fabricating phase-pure and uniaxially oriented perovskite films.

A novel electron transport layer (ETL) combining indene-C60 bisadduct and a non-fullerene n-type polymer is developed. Leveraging the high electron mobility, favorable band structure, robust interaction with Sn-based perovskites, and elongated alkyl side chains of this polymer, the Sn-based perovskite solar cell incorporating the novel ETL demonstrates a notable enhancement in power conversion efficiency to 13.90% alongside excellent stability.

Abstract

With excellent biocompatibility, a narrow bandgap, and long thermal carrier lifetime, tin-based perovskite solar cells (TPSCs) are promising within the solar technology. The fullerene derivative indene-C₆₀ bisadduct (ICBA) is recognized as the most efficient electron-transport material for TPSCs, thanks to its suitable band structure. Nevertheless, the limited electron transport capability and susceptibility to moisture penetration of ICBA have hindered the progress of TPSCs. Herein, the study proposes a new hydrophobic electron-transport layer (ETL) comprising a surface-anchored non-fullerene n-type semiconducting polymer layer, poly (naphthalene diimide-alt-dithiophenebezothiadiazole) (PNDI-BT), in conjunction with ICBA. PNDI-BT exhibits high electron mobilities, a fitting band structure, robust interaction with Sn-based perovskites, and exceptional moisture resistance, effectively addressing the shortcomings of ICBA. Consequently, this innovative hydrophobic ETL of PNDI-BT/ICBA enhances electron transport and protects Sn-based perovskites from moisture. As a result, the inverted TPSCs with the new hydrophobic ETL achieve an impressive efficiency of 13.90%, surpassing TPSCs with the ICBA layer (12.75%). Moreover, even after 1000 h of storage in ambient atmosphere, the encapsulated TPSC maintains a remarkable 81% of its initial efficiency. This comprehensive study seamlessly integrates the synthesis of non-fullerene n-type semiconducting polymer and device fabrication, providing valuable insights into designing cutting-edge ETL structure for inverted TPSCs.

A facile strategy is reported to systematically manipulate the crystallization and passivate defects by incorporating robust dual-functional additives. The additive not only regulates crystallization kinetics but acts as a passivator, effectively passivating defects, releasing residual strain, and achieving a favorable n-type contact interface. The resultant devices accomplish a power conversion efficiency (PCE) of 24.05% and an ultra-high fill factor (FF) of 84.22% with improved stability.

Abstract

Inverted perovskite solar cells (PSCs) comprising formamidinium-cesium (FA-Cs) lead triiodide have garnered considerable attention due to their impressive efficiency and remarkable stability. Nevertheless, synthesizing high-quality FA-Cs alloyed perovskite films presents challenges, primarily attributable to the intricate interphase process involved and the absence of methylammonium (MA⁺) and mixed halogens. Here, the additive 3-phosphonopropanoic acid (3-PPA) is introduced, with bifunctional phosphonic acid groups, into the perovskite precursor to modulate the crystal growth and provide passivation at grain boundaries. In situ characterization reveals that the 3-PPA can form a “rapid nucleation, slow growth” mechanism, resulting in perovskite films with enlarged grains and enhanced crystallinity. In addition, 3-PPA serves to passivate grain boundary defects and release residual strain by forming molecular bridging, leading to the passivated films achieving a fluorescence lifetime of 5.79 microseconds with a favorable n-type contact interface. As a result, the resulting devices incorporating 3-PPA achieve a champion power conversion efficiency (PCE) of 24.05% and an ultra-high fill factor (FF) of 84.22%. More importantly, the optimized devices exhibit satisfactory stability under various testing conditions. The findings underscore the pivotal role of multifunctional additives in crystallization control and defect passivation for high-performance MA-free and pure iodine PSCs.

Surface passivation reduces non-radiative charge recombination and interfacial charge accumulation in perovskite photovoltaics. Carbazole, functionalized with ammonium iodide and alkyl chains, forms hydrophobic passivation layers on FAPbI₃ perovskite films, improving stability and efficiency. This approach minimizes trap-assisted recombination and enhances hole transfer, achieving 24.8% PCE and maintaining 95% of its initial efficiency after 1000 h under the ISOS-L1 protocol.

Abstract

Surface passivation has been widely employed to suppress non-radiative charge recombination and prevent interfacial charge accumulation in perovskite photovoltaics. In this report, carbazole modified with ammonium iodide connected via alkyl chains of different lengths (i.e., ethyl, butyl, and hexyl chains) is used to form passivation layers on formamidinium lead triiodide FAPbI₃-based perovskite films to improve operational stability. Owing to the strong hydrophobicity of the carbazole moiety, it is observed that the perovskite films with a carbazole passivation layer retain their initial properties even after direct contact with a water droplet for 100 s. In addition, carbazole treatment reduces the rate of trap-assisted recombination at the surface and grain boundaries of the perovskite layer. Furthermore, it accelerates interfacial hole transfer from the perovskite to the charge transport layer. As a result, devices treated with carbazole hexylammonium iodide achieve a power conversion efficiency (PCE) of up to 24.3% during quasi-steady-state (QSS) measurements with extraordinary long-term operational stability under conditions of the ISOS-L-1 protocol, maintaining 95% of their initial efficiency after 1000 h.

Quinoxaline (Qx)-based nonfullerene acceptors (QxNFAs) enable the power conversion efficiency of organic solar cells approaching 20%. In order to effectively develop QxNFAs, the advances of QxNFAs are highlighted, the relationships between molecular structure and photovoltaic performance are analyzed, and strategies to the challenges are proposed.

Abstract

In the recent advances of organic solar cells (OSCs), quinoxaline (Qx)-based nonfullerene acceptors (QxNFAs) have attracted lots of attention and enabled the recorded power conversion efficiency approaching 20%. As an excellent electron-withdrawing unit, Qx possesses advantages of many modifiable sites, wide absorption range, low reorganization energy, and so on. To develop promising QxNFAs to further enhance the photovoltaic performance of OSCs, it is necessary to systematically summarize the QxNFAs reported so far. In this review, all the focused QxNFAs are classified into five categories as following: SM-Qx, YQx, fused-YQx, giant-YQx, and polymer-Qx according to the molecular skeletons. The molecular design concepts, relationships between the molecular structure and optoelectronic properties, intrinsic mechanisms of device performance are discussed in detail. At the end, the advantages of this kind of materials are summed up, the molecular develop direction is prospected, the challenges faced by QxNFAs are given, and constructive solutions to the existing problems are advised. Overall, this review presents unique viewpoints to conquer the challenge of QxNFAs and thus boost OSCs development further toward commercial applications.