Chen Weijie

A bilayer comprising of nickel phthalocyanine (NiPc) and poly(3-hexylthiophene) (P3HT) serves as the hole transport material in perovskite solar cells. P3HT shows vertical phase separation during coating. Precise adjustment of P3HT-NiPc ratio yields a remarkable 23.11% power conversion efficiency. Encapsulation in polyisobutylene ensures exceptional long-term stability with 90% of initial efficiency retained after exposure to 85 °C and 85% relative humidity for 1000 h.

Abstract

To expedite the commercialization of perovskite solar cells (PSCs), researchers are exploring the feasibility of employing nickel phthalocyanine (NiPc) as a hole transport material (HTM) due to its cost-effectiveness, excellent thermal stability, and suitability for solution coating. However, the low LUMO energy level of the NiPc may limit its ability to block photoelectrons generated in the perovskite layer from recombining with holes, which can reduce the overall efficiency of the solar cell. One solution is to use cascaded bilayers with HTMs that have relatively higher LUMO levels. In this study, a bilayer consisting of NiPc and poly(3-hexylthiophene) (P3HT) is employed as the HTM, where the P3HT exhibits vertical phase separation during the coating process. By optimizing the mixing amount of P3HT into the NiPc, a record power conversion efficiency of 23.11%, the highest reported for NiPc-based PSCs is achieved. Moreover, an excellent long-term stability is demonstrated by encapsulating the PSC in polyisobutylene, with the device retaining 90% of its initial efficiency after exposure to 85 °C and 85% relative humidity for 1000 h.

A series of new regioisomeric dimerized small-molecule acceptors (DSMAs; DYA-I, DYA-IO, and DYA-O) with acetylene linkers is developed. The organic solar cells (OSCs) using DYA-I exhibit a high-power conversion efficiency (PCE) of 18.8% and exceptional long-term stability, with an extrapolated t _80% lifetime exceeding 5000 h under 1-sun illumination. These results underline the commercial potential of DSMA-derived OSCs.

Abstract

The commercialization of organic solar cells (OSCs) requires both high power conversion efficiency (PCE) and long-term stability. However, the lifetime of the OSCs containing small-molecule acceptors (SMA) should be significantly enhanced. In this study, a series of planarity-controlled is developed, high electron mobility dimerized SMAs (DSMAs) and realize OSCs with high-performance (PCE = 18.8%) and high-stability (t _80% lifetime = 5380 h under 1-Sun illumination). An acetylene linker with a planar triple bond is designed for dimerization of SMA units to afford the high backbone planarity necessary to achieve high crystallinity and electron mobility. To further engineer the molecular conformation and electron mobility of the DSMAs, different regioisomers of a Y-based SMA are dimerized to yield three regioisomerically distinct DSMAs, denoted as DYA-I, DYA-IO, and DYA-O, respectively. It is found that the crystallinity, electron mobility, and glass transition temperature of the DSMAs gradually increase in the order of DYA-O, DYA-IO, and DYA-I, which, in turn, enhance the PCE and device stability of the resulting OSCs; DYA-O (PCE = 16.45% and t _80% lifetime = 3337 h) < DYA-IO (PCE = 17.54% and t _80% lifetime = 4255 h) < DYA-I (PCE = 18.83% and t _80% lifetime = 5380 h).

Using a hybrid two-step deposition method, prepared robust 2D perovskites with cross-linkable ligands underneath 3D perovskite enable the formation of a conformal 2D/3D heterostructure at the buried interface. Owing to the influence of the heterojunction on crystallization and interfacial modulation, perovskite–silicon tandem solar cells based on industrially fully textured silicon achieve an efficiency of 29.8% (certified 28.4%).

Abstract

Exploring strategies to control the crystallization and modulate interfacial properties for high-quality perovskite film on industry-relevant textured crystalline silicon solar cells is highly valued in the perovskite/silicon tandem photovoltaics community. The formation of a 2D/3D perovskite heterojunction is widely employed to passivate defects and suppress ion migration in the film surface of perovskite solar cells. However, realizing solution-processed heterostructures at the buried interface faces solvent incompatibilities with the challenge of underlying-layer disruption, and texture incompatibilities with the challenge of uneven coverage. Here, a hybrid two-step deposition method is used to prepare robust 2D perovskites with cross-linkable ligands underneath the 3D perovskite. This structurally coherent interlayer benefits by way of preferred crystal growth of strain-free and uniform upper perovskite, inhibits interfacial defect-induced instability and recombination, and promotes charge-carrier extraction with ideal energy-level alignment. The broad applicability of the bottom-contact heterostructure for different textured substrates with conformal coverage and various precursor solutions with intact properties free of erosion are demonstrated. With this buried interface engineering strategy, the resulting perovskite/silicon tandem cells, based on industrially textured Czochralski (CZ) silicon, achieve a certified efficiency of 28.4% (1.0 cm²), while retaining 89% of the initial PCE after over 1000 h operation.

Modulating the charge-transport behavior of hole-transport materials (HTMs) is a path toward improved hole mobility and enhanced device properties when used in solar cells. Here, we design a porphyrin supramolecule to modulate the surface properties of the commonly used Spiro-OMeTAD HTM in perovskite solar cells. Upon doping monoamine Fe^III porphyrin into Spiro-OMeTAD, the porphyrins self-assemble into oxygen-bridged dimer-based supramolecules located at the grain boundaries of the HTM. The doped perovskite devices exhibit an increased efficiency from 19.8 % to 23.2 %, and greatly improved stability.

Abstract

Modulating the surface charge transport behavior of hole transport materials (HTMs) would be as an potential approach to improve their hole mobility, while yet realized for fabricating efficient photovoltaic devices. Here, an oxygen bridged dimer-based monoamine Fe^III porphyrin supramolecule is prepared and doped in HTM film. Theoretical analyses reveal that the polaron distributed on dimer can be coupled with the parallel arranged polarons on adjacent dimers. This polaron coupling at the interface of supramolecule and HTM can resonates with hole flux to increase hole transport efficiency. Mobility tests reveal that the hole mobility of doped HTM film is improved by 8-fold. Doped perovskite device exhibits an increased efficiency from 19.8 % to 23.2 %, and greatly improved stability. This work provides a new strategy to improve the mobility of HTMs by surface carrier modulation, therefore fabricating efficient photovoltaic devices.

The co-solvent strategy to disassemble the micelles formed by the amphiphilic self-assembled monolayer (SAM) molecules is introduced. The pre-disassembly of micelles reduces the energetic barrier to form a densely packed SAM. This strategy universally enhances the power conversion efficiencies (PCEs) of PSCs based on MeO-2PACz, 2PACz, and CbzNaph SAM hole-selective layers. The champion device based on the CbzNaph processed from co-solvent achieves a high PCE of 24.98% with an impressive fill factor of 85.06%.

Abstract

Self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). However, most SAM molecules are amphiphilic in nature and tend to form micelles in the commonly used alcoholic processing solvents. This introduces an extra energetic barrier to disassemble the micelles during the binding of SAM molecules on the substrate surface, limiting the formation of a compact SAM. To alleviate this problem for achieving optimal SAM growth, a co-solvent strategy to disassemble the micelles of carbazole-based SAM molecules in the processing solution is developed. This effectively increases the critical micelle concentration to be above the processing concentration and enhances the reactivity of the phosphonic acid anchoring group to allow densely packed SAMs to be formed on indium tin oxide. Consequently, the PSCs derived from using MeO-2PACz, 2PACz, and CbzNaph SAM HSLs show universally improved performance, with the CbzNaph SAM-derived device achieving a champion efficiency of 24.98% and improved stability.

A solution-processed sandwich structure silver-nanowires top electrode is designed for semi-transparent organic photovoltaics (ST-OPVs) to address conductivity and processibility issues. Compared with traditional evaporated Ag counterpart, ST-OPV based on the new electrode achieves more excellent optical and electrical properties, including light utilization efficiency, transmittance, reflection rate, viewing angle, and can tolerate harsher mechanical bending on flexible substrates.

Abstract

Photovoltaic windows with easy installation for the power supply of household appliances have long been a desire of energy researchers. However, due to the lack of top electrodes that offer both high transparency and low sheet resistance, the development of high-transparency photovoltaic windows for indoor lighting scenarios has lagged significantly behind photovoltaic windows where privacy issues are involved. Addressing this issue, this work develops a solution-processable transparent top electrode using sandwich structure silver nanowires, realizing high transparency in semi-transparent organic solar cells. The wettability and conducting properties of the electrode are improved by a modified hole-transport layer named HP. The semi-transparent solar cell exhibits good see-through properties at a high average visible transmittance of 50.8%, with power conversion efficiency of 7.34%, and light utilization efficiency of 3.73%, which is the highest without optical modulations. Moreover, flexible devices based on the above-mentioned architecture also show excellent mechanical tolerance compared with Ag electrode counterparts, which retains 94.5% of their original efficiency after 1500 bending cycles. This work provides a valuable approach for fabricating solution-processed high transparency organic solar cells, which is essential in future applications in building integrated photovoltaics.

Nature Energy, Published online: 25 July 2023; doi:10.1038/s41560-023-01337-1

Polylactic acid (PLA) is used to modify mixed-halide inorganic perovskites. PLA can passivate the defects and induce n-type to p-type transition, favoring charge transfer from perovskite to hole transport layer, thus improving the device performance. Record power conversion efficiencies of 19.12% and 18.05% are achieved for CsPbI_2.25Br_0.75 and CsPbI₂Br solar cells, respectively.

Abstract

Inorganic perovskite solar cells (PSCs) suffer from serious carrier recombination and open-circuit voltage loss because of surface defects and unfavorable energy level alignment. Herein, a polylactic acid (PLA) modification approach to improve the performance of mixed-halide inorganic perovskites is reported. First, the surface defects are effectively passivated through strong interaction between C═O in PLA and undercoordinated Pb²⁺. Second, secondary grain growth is induced by PLA modification, resulting in larger grain sizes. Third, PLA modification makes the surface region of perovskite change from n- to p-type, favoring charge transport from perovskite to the hole transport layer (HTL). The PLA modified films enable PSCs with less nonradiative recombination and lower energy loss. Consequently, record PCEs of 19.12% and 18.05% are achieved for CsPbI_2.25Br_0.75 and CsPbI₂Br PSCs, respectively. The PSC with an active area of 1 cm² shows a PCE of 16.41%. A PCE of 14.70% is achieved for HTL-free PSC with carbon electrode. In addition, the PSC with PLA modification shows significantly improved air stability due to the hydrophobic PLA coating. This work suggests that PLA surface modification is an effective approach to achieving efficient, stable, scalable, and low-cost inorganic PSCs.

Nature, Published online: 24 July 2023; doi:10.1038/s41586-023-06450-5

Herein, indium zinc tin oxide (IZTO) serves as the bottom electrode in a flexible indoor organic photovoltaic (OPV) system, showing high effectiveness and mechanical robustness. With superior mechanical stability, the IZTO-based flexible OPV retains 69% of its initial power conversion efficiency (15.16%) even after 100 000 bend repetitions under 1000 lx LED illumination.

The demand for flexible indoor organic photovoltaic cells (OPVs) is growing dramatically due to their simple and practical use as a powering aid for various electronic gadgets connected to the Internet of Things. Due to the brittleness of inorganic material-based transparent bottom electrodes and their incompatibility with flexible organic substrates, it is extremely difficult to limit the influence of mechanical stress on the stability of flexible OPV. In this regard, choosing a mechanically stable and highly conductive transparent conducting oxide (TCO) is crucial. Therefore, flexible OPVs are fabricated onto a flexible (polyimide) substrate coated with mechanically stable TCO indium zinc tin oxide (IZTO). Sheet resistance measurements and observations of scanning electron microscope images of IZTO film after 100 000 bending repetitions (bending radius: 5 mm) confirm the ultrahigh mechanical stability of the TCO. The sheet resistance of flexible IZTO electrode layers is increased by 9%, from 17.42 to 19.12 Ω sq⁻¹. In addition, the impact of a large number of bending repetitions on film transmittance is minimal. The OPV shows ≈69% and ≈20% of its initial power conversion efficiency value after 100 000 bending repetitions for 1000 lx LED illumination and 1 sun conditions, respectively.

A pressure-assisted fast crystallization technique is introduced for high-efficiency perovskite solar cells. This technique not only reduces the thermal annealing period to less than 2 min but also achieves the impressive formation of micrometer-sized vertical-monolithic perovskite crystals. As a result, power conversion efficiency is enhanced from 22.49% to 24.69%, and this crystallization approach is universal and highly reproducible for solution-processed manufacturing methods.

The achievement of high-performance solar cell production hinges on the development of a reliable and effective approach for perovskite crystallization that is compatible with rapid and continuous processing on large substrates. Herein, a pressure-assisted fast crystallization technique is presented that reduces the thermal annealing period to less than 2 min and achieves the impressive formation of micrometer-sized vertical-monolithic perovskite crystals. The pressure-assisted technique provides confined space and pressure, where the confined space hinders the volatilization of residual solvents and enhances the Ostwald ripening effect. The presence of pressure provides internal energy for crystal growth, while the presence of solvent molecules accelerates solute diffusion. These factors collectively contribute to the rapid growth of grains. Results demonstrate that this pressure-assisted fast crystallization strategy significantly enhances the power conversion efficiency (PCE) of both n-i-p and p-i-n perovskite solar cells (PSCs), achieving PCEs of 22.80% and 24.69%, respectively. The improvement in PCE can be attributed to the reduced number of grain boundaries, minimized interfacial defects, and enhanced surface crystalline quality. Importantly, this approach is universal and highly reproducible for solution-processed manufacturing methods. It is anticipated that this efficient, reliable, and reproducible technique will accelerate the commercialization of PSCs.

Ytterbium fluoride (YbF₃) is introduced as a multifunctional additive for perovskite precursor solution. The addition of YbF₃ improved the quality, passivated the defects, and improved the stability of perovskite film. At the same time, the power conversion efficiency (PCE) of perovskite solar cell is also improved. By using YbF₃ as additive, the device is prepared with a champion PCE of 24.53%.

Abstract

With better light utilization, larger tolerance factor, and higher power conversion efficiency (PCE), the HC(NH₂)₂ ⁺(FA)-based perovskite is proven superior to the popular CH₃NH₃ ⁺ (MA)- and Cs-based halide perovskites in solar cell applications. Unfortunately, limited by intrinsic defects within the FA-based perovskite films, the perovskite films can be easily transformed into a yellow δ-phase at room temperature in the fabrication process, a troublesome challenge for its further development. Here, ytterbium fluoride (YbF₃) is introduced into the perovskite precursor for three objectives. First of all, the partial substitution of Yb³⁺ for Pb²⁺ in the perovskite lattice increases the tolerance factor of the perovskite lattice and facilitates the formation of the α phase. Second, YbF₃ and DMSO in the solvent form a Lewis acid complex YbF₃·DMSO, which can passivate the perovskite film, reduce defects, and improve device stability. Consequently, the YbF₃ modified Perovskite solar cell exhibits a champion conversion efficiency of 24.53% and still maintains 90% of its initial efficiency after 60 days of air exposure under 30% relative humidity.

The study demonstrates how strong local-exciton (LE)-charge-transfer (CT) hybridization in low-energy offset bulk-heterojunctions results in ultra-fast CT state formation via direct photoexcitation. These strongly intermixed and emissive LE-CT states accelerate the recombination of both CT and charge separated (CS) states. Moreover, the application of an external electric field can significantly weaken the LE-CT hybridization, enhancing CT and CS state yield but attenuating device emission efficiency.

Abstract

In organic solar cells with very small energetic-offset (ΔE_{LE − CT}), the charge-transfer (CT) and local-exciton (LE) states strongly interact via electronic hybridization and thermal population effects, suppressing the non-radiative recombination. Here, we investigated the impact of these effects on charge generation and recombination. In the blends of PTO2:C8IC and PTO2:Y6 with very small, ultra-fast CT state formation was observed, and assigned to direct photoexcitation resulting from strong hybridization of the LE and CT states (i.e., LE-CT intermixed states). These states in turn accelerate the recombination of both CT and charge separated (CS) states. Moreover, they can be significantly weakened by an external-electric field, which enhanced the yield of CT and CS states but attenuated the emission of the device. This study highlights that excessive LE-CT hybridization due to very low , whilst enabling direct and ultrafast charge transfer and increasing the proportion of radiative versus non-radiative recombination rates, comes at the expense of accelerating recombination losses competing with exciton-to-charge conversion process, resulting in a loss of photocurrent generation.

Publication date: November 2023

Source: Journal of Energy Chemistry, Volume 86

Author(s): Qi Cao, Yixin Zhang, Xingyu Pu, Junsong Zhao, Tong Wang, Kui Zhang, Hui Chen, Xilai He, Jiabao Yang, Cheng Zhang, Xuanhua Li

Publication date: October 2023

Source: Journal of Energy Chemistry, Volume 85

Author(s): Zenghua Wang, Bing Cai, Deyu Xin, Min Zhang, Xiaojia Zheng

The substituent position of alkyls matters! Internal hexyl substitution, in contrast to terminal substitution, weakens π─π stacking but enhances molecular packing density. This improves film morphology, boosts hole conduction, reduces diffusion of external species, and notably raises the glass temperature, enabling the fabrication of thermostable perovskite solar cells with an average efficiency surpassing 24%.

Abstract

Polycyclic aromatic hydrocarbons play a critical role in the development of organic semiconductors. This study unravels the impact of alkyl substitution position on the molecular energy level, glass transition temperature, diffusion of external species, and hole transport of a pyrrole-rich, helical polycyclic heteroaromatic, that is TBPC. Compared to terminal substitution, internal hexyl substitution results in steric repulsion with TBPC, weakening π─π stacking and therefore improving thin film morphology. Internal substitution also reduces energy disorder, lowers reorganization energy, and increases intermolecular transfer integrals, leading to enhanced hole mobility. Notably, the organic semiconductor with internal hexyl substitution (TBPC-611) exhibits a higher molecular packing density, resulting in a markedly higher glass transition temperature and slower diffusion of external species. Using TBPC-611 as the hole transport material, this work successfully fabricates perovskite solar cells with an average power conversion efficiency above 24%, showing good photostability and thermostability. These findings contribute new insights to the development of high-performance organic semiconductors.

PM6 polycrystals are incubated through a vapor diffusion method and redissolved in chloroform to prepare PM6 pre-aggregates, which can increase the structural order of both the donors and the acceptors in photovoltaic blends upon solution casting, consequently delivering high performance for both thin and thick junction organic solar cells.

Abstract

Organic semiconductors are generally featured with low structure order in solid-state films, which leads to low charge-transport mobility and strong charge recombination in their photovoltaic devices. In this work, a “polycrystal-induced aggregation” strategy orders the polymer donor (PM6) and non-fullerene acceptor (L8-BO) molecules during solution casting with the assistance of PM6 polycrystals that are incubated through a vapor diffusion method, toward improved solar cell efficiency with either thin or thick photoactive layers. These PM6 polycrystals are redissolved in chloroform to prepare PM6 pre-aggregates (PM6-PA), and further incorporated into the conventional PM6:L8-BO blend solutions, which is found to prolong the molecular organization process and enhance the aggregation of both the PM6 and the L8-BO components. As the results, with the assistance of 10% PM6-PA, PM6:L8-BO solar cell devices obtain power conversion efficiencies (PCEs) from 18.0% and 16.2% to 19.3% and 17.2% with a 100 nm-thick and 300 nm-thick photoactive layer, respectively.

A vapor deposition method in combination with a solvent-assisted recrystallization technique is presented to fabricate high-quality larger-area perovskite film. Efficiency of 19.9% is achieved, which is among the highest values ever reported for minimodules based on vapor-deposited perovskite.

Abstract

Vapor deposition is a promising technology for the mass production of perovskite solar cells. However, the efficiencies of solar cells and modules based on vapor-deposited perovskites are significantly lower than those fabricated using the solution method. Emerging evidence suggests that large defects are generated during vapor deposition owing to a specific top-down crystallization mechanism. Herein, a hybrid vapor deposition method combined with solvent-assisted recrystallization for fabricating high-quality large-area perovskite films with low defect densities is presented. It is demonstrated that an intermediate phase can be formed at the grain boundaries, which induces the secondary growth of small grains into large ones. Consequently, perovskite films with substantially reduced grain boundaries and defect densities are fabricated. Results of temperature-dependent charge-carrier dynamics show that the proposed method successfully suppresses all recombination reactions. Champion efficiencies of 21.9% for small-area (0.16 cm²) cells and 19.9% for large-area (10.0 cm²) solar modules under AM 1.5 G irradiation are achieved. Moreover, the modules exhibit high operational stability, i.e., they retain >92% of their initial efficiencies after 200 h of continuous operation.

Herein, the application of a modeling framework for the optimal design of color photovoltaic (PV) modules is presented based on optical filters. It combines colorimetric analysis and advanced PV performance modeling to provide design guidelines to produce beautiful modules with excellent color stability by analyzing different front- and backside glass texturing options.

Herein, the application of a comprehensive modeling framework that can help optimize the design of multilayered optical filters for coloring photovoltaic (PV) modules is presented based on crystalline silicon solar cells. To overcome technical issues related to the implementation of color filters (CFs) on PV modules, like glare and color instability, colorimetry metrics, such as the hue, chroma, luminance color space, and the quantitative concept of difference between two colors are extensively deployed. It is showcased in this work that designing colored modules with high hue and chroma stability is possible by using a front-side texturing with edged geometry, like V-shaped grooves and inverted pyramids, while obtaining colors with relatively high luminance values, indicating good brightness. Furthermore, it is argued that adapting the rear surface of the front glass with a random textured layout where the CF is applied can improve color and luminance stability without significant loss of chroma while eliminating glare. Finally, the models can be used to optimize the number of layers for a given CF, reducing unnecessary optical losses. Compared to a standard PV module, performance simulation of optimized, bright-colored PV modules predicts relative energy yield losses ranging from 7% to 25%.

Herein, efficiency improvements in various single-junction solar cells are reviewed in this article and several losses of high-efficiency single-junction solar cells are discussed. Perspective of single-junction solar cells from the viewpoint of practically feasible efficiency based on scientific and technological arguments is also presented. In addition, problems to be solved for solar cell modules are discussed.

Photovoltaic energy conversion is expected to contribute to creation of a clean energy society and high-performance solar cells are very attractive for realizing such a vision. The development of high-performance solar cells offers a promising pathway toward achieving high power per unit cost for many applications. Although state of the art of some of single-junction solar cells are approaching the Shockley–Queisser limit of 32–33%, further improvements in efficiencies of solar cell and modules are thought to be possible. Herein, efficiency improvements in various single-junction solar cells are overviewed in this article and several losses of high-efficiency single-junction solar cells are discussed about. Perspective of single-junction solar cells from the viewpoint of practically feasible efficiency based on scientific and technological arguments is also presented. In addition, problems to be solved for solar cell modules are discussed.

Based on the machine-learning model and empirical descriptors, the author proposes a data-driven approach to predict the electrical performance of nonfullerene organic solar cells (OSCs) and reveal their charge transfer behaviors. The results show that the lowest unoccupied molecular orbital offset (between donor and acceptor) plays the most significant role in increasing the short-circuit current density values of nonfullerene OSCs.

An efficient computational approach, in contrast to the trial-and-error experiment process, for predicting, characterizing, and optimizing the macroscopic performance parameters (e.g., short-circuit current density (J _sc)) of nonfullerene acceptors-based organic solar cells (OSCs) remains a rarely addressed and complicated challenge. In this work, a data-driven approach is used to predict the electrical performance of nonfullerene OSCs and reveal their charge transfer behaviors. The eXtreme Gradient Boosting (XGBoost) model within empirical descriptors is used to understand the governing feature for enhancement of J _sc, which is vital for the design and discovery of new donor/nonfullerene acceptor photoactive layers for photovoltaic applications. Through the well-trained XGBoost model and SHapley Additive exPlanations theory, the descriptors impacting the J _sc of nonfullerene OSCs are further explained and analyzed. Remarkably, the XGBoost model combines four empirical descriptors to achieve an impressive prediction accuracy (R ² > 0.8). The results from data-driven approaches prove that the lowest unoccupied molecular orbital (LUMO) offset (between donor and acceptor) plays the most significant role in increasing the J _sc values of nonfullerene OSCs. Moreover, this study highlights the effect of LUMO offset on the photoinduced charge transfer process of donor/non-fullerene acceptor blends, which might pave the way toward rapid and precise energy-level tuning of efficient OSC materials.

Benzimidazole (BIm) is first introduced into the Y6 skeleton as a central core to construct two new non-fullerene acceptors, MZ-1 and MZ-2. In contrast to MZ-1, MZ-2 with trifluoromethylation on the BIm 2C position gives excellent photovoltaic performance with a higher PCE of 17.31%.

Abstract

Electron-deficient central core plays a crucial role in the construction of efficient Y-series non-fullerene acceptors (NFAs). Here, fused-ring benzimidazole (BIm) served as a central core for the first time to yield a new NFA named MZ-1 and its structural analogue named MZ-2, which is obtained by replacing the methyl group on the 2C position of BIm in MZ-1 with trifluoromethyl group. Compared with MZ-1, MZ-2 shows obviously blue-shifted absorption and lowers the highest occupied molecular orbital (HOMO) energy level that is more matched to that of polymer donor PM6. Benefiting from the more efficient charge transport and favorable microphase separation morphology of the active layer, the acceptor MZ-2-based device affords an excellent power conversion efficiency (PCE) of 17.31% along with a high open-circuit voltage (V _oc) of 0.903 V, a short-circuit current density (J _sc) of 26.32 mA cm⁻² and a fill factor (FF) of 72.83%, which is remarkably superior to that of MZ-1-based devices with PCE of 10.70%. This study offers valuable insight into the design of acceptors to enrich Y series NFAs for high-performance organic solar cells (OSCs).