Yingzhi Jin

All-polymer solar cells (all-PSCs) are attractive as alternatives to fabricate thermally and mechanically stable solar cells, especially with recent improvements in their power conversion efficiency (PCE). In this work, efficient all-PSCs with near-infrared response (up to 850 nm) are developed using newly designed regioregular polymer donors with relatively narrow optical gap. These all-PSCs systems achieve PCEs up to 6.0% after incorporating fluorine into the polymer backbone. More importantly, these polymers exhibit absorbance that is complementary to previously reported wide bandgap polymer donors. Thus, the superior properties of the newly designed polymers afford opportunities to fabricate the first spectrally matched all-polymer tandem solar cells with high performance. A PCE of 8.3% is then demonstrated which is the highest efficiency so far for all-polymer tandem solar cells. The design of narrow bandgap polymers provides new directions to enhance the PCE of emerging single-junction and tandem all polymer solar cells.

By adopting D1-A-D2-A ternary structure, a pair of novel regioregular polymers, namely PBBSB and PBFSF, are synthesized. Benefiting from the new arrangement and molecular fluorination, the polymer exhibits relatively narrow optical gap, good intermolecular packing, and excellent charge transport. More importantly, it is shown that these functional donor polymers can achieve high efficiency in either single-junction or tandem all-polymer solar cells.

This review provides an up-to-date review about the small molecule interlayers (SMIs) in organic solar cells (OSCs). Compared to polymer interlayers, SMIs exhibit intrinsic advantages such as easy synthesis and purification, monodispersity, well-defined chemical structure, and high batch-to-batch reproducibility. Recently, various SMIs have been reported with landmark efficiencies of over 10% in both conventional and inverted OSCs, exhibiting promising potential in commercial application. In this review, the authors summarize the progress of SMIs from a device fabrication point of view, paying particular attention to the material categories, molecular design, preparation process, and applicable device structure. In addition, the working mechanisms of different SMIs are also discussed, including the structure–property relationships and the corresponding impact on device performance. Finally, a brief outlook is provided that includes opportunities and challenges in this emerging area.

Small molecule interlayers (SMIs) have attracted considerable attention in organic solar cells due to their simple syntheses, well-defined structures, and high batch-to-batch reproducibility. This article provides an overview of SMIs from a device fabrication point of view, focusing on the material categories, preparation methods, film properties, and applicable device configurations. The structure–property relationships and their impact on device performance are also discussed.

Molecular packing structures in the active layers have a crucial impact on the electronic processes for organic solar cells. To date, however, it is still difficult to probe molecular self-assembling and packing structures at the atomic level by experimental techniques, which is hindering reliable understanding of the structure–property relationship. Accordingly, theoretical simulations provide a useful tool and are becoming more and more important. Here, recent advances in theoretical simulations for organic solar cells are reviewed. First, a brief introduction of theoretical methodologies, including the strategies of molecular dynamics simulations of active-layer processing procedures and quantum-chemical methods for calculating electron transfer processes, is given. Then, the influences of molecular packing structures on charge generation, charge recombination, and charge transport are analyzed and discussed from a theoretical perspective. Finally, prospects and challenges are pointed out for theoretical prediction of the electrical characteristics and photoelectric conversion efficiencies of organic solar cells from molecular structures.

Recent advances in theoretical simulations for organic solar cells are summarized, ranging from molecular packing structures to electronic processes. Insights into the correlation between molecular structures, molecular packing morphologies, and electronic processes are provided, which would be helpful to molecular design toward improving photovoltaic performance.

In article number 1701436 by Bumjoon J. Kim and co-workers, a series of naphthalenediimide-based polymer acceptors with superior electron mobility and large dipole moment difference is developed by incorporating electron-withdrawing cyanovinylene groups into a polymer backbone. All-polymer solar cells based on these polymers generate outstanding power conversion efficiency of 7.4% with high fill factor (65%), by virtue of the high electron transport and efficient exciton dissociation with greatly suppressed charge recombination.

The stability of donor:acceptor (D:A) semiconductor blends plays a key role in the development of solution-processed organic solar cells. One essential condition for both high-yield production and a long lifetime is excellent thermal stability. Recently, A₁:A₂ acceptor mixtures have received considerable attention and alloys of two miscible acceptors are singled out as a powerful tool for the design of efficient and durable organic solar cells. This progress report introduces a thermodynamic rationale for the superior thermal stability and reproducibility that is observed for some ternary blends. The increase in entropy upon mixing of several acceptors reduces the tendency for phase separation as well as crystallization, which facilitates the controlled formation of a fine blend nanostructure. Further, when combined with a high glass transition temperature many ternary blends can be readily quenched into a glassy state. Recent progress with regard to the thermal stability and efficiency of D:A₁:A₂ ternary blends is summarized in the light of the thermodynamic and kinetic arguments discussed in this article. Both, fullerene and fullerene-free acceptor alloys now yield solar cell efficiencies in excess of 10%, which indicates that ternary blends are a promising avenue that is poised to considerably enhance the prospect of organic photovoltaics.

Ternary organic solar cells display superior thermal stability and reproducibility. The increase in entropy upon mixing of several acceptors reduces the tendency for phase separation and crystallization. When combined with a high glass transition temperature many ternary blends can be quenched into a glassy state. Both, fullerene and fullerene-free acceptor alloys now yield solar cell efficiencies in excess of 10%.

Optimizing the interfacial contacts between the photoactive layer and the electrodes is an important factor in determining the performance of organic solar cells (OSCs). A charge-selective layer with tailored electrical properties enhances the charge collection efficiency and interfacial stability. Here, the potential of hydrogenated TiO₂ nanoparticles (H-TiO₂ NPs) as an efficient electron-selective layer (ESL) material in OSCs is reported for the first time. The H-TiO₂ is synthesized by discharge plasma in liquid at atmospheric pressure, which has the benefits of a simple one-pot synthesis process, rapid and mild reaction conditions, and the capacity for mass production. The H-TiO₂ exhibits high conductivity and favorable energy level formation for efficient electron extraction, providing a basis for an efficient bilayer ESL system composed of conjugated polyelectrolyte/H-TiO₂. Thus, the enhanced charge transport and extraction efficiency with reduced recombination losses at the cathode interfacial contacts is achieved. Moreover, the OSCs composed of H-TiO₂ are almost free of light soaking, which has been reported to severely limit the performance and stability of OSCs based on conventional TiO₂ ESLs. Therefore, H-TiO₂ as a new efficient, stable, and cost-effective ESL material has the potential to open new opportunities for optoelectronic devices.

This study demonstrates the potential of hydrogenated TiO₂ (H-TiO₂) as an efficient electron-selective layer in optoelectronic devices. The H-TiO₂ is simply one-pot mass-produced using a discharge plasma system in liquid at atmospheric pressure. The H-TiO₂ exhibits high conductivity and favorable energy level formation, resulting in the high-efficiency and light-soaking-free organic solar cells.

The morphology of the active layer of a bulk heterojunction solar cell, made of a blend of an electron-donating polymer and an electron-accepting fullerene derivative, is known to play a determining role in device performance. Here, a combination of molecular dynamics simulations and long-range corrected density functional theory calculations is used to elucidate the molecular-scale effects that even minor structural changes to the polymer backbone can have on the “local” morphology; this study focuses on the extent of polymer–fullerene mixing, on their packing, and on the characteristics of the fullerene–fullerene connecting network in the mixed regions, aspects that are difficult to access experimentally. Three representative polymer donors are investigated: (i) poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)] (PffBT4T-2OD); (ii) poly[(2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)] (PBT4T-2OD), where the fluorine atoms in the benzothiadiazole moieties of PffBT4T-2OD are replaced with hydrogen atoms; and (iii) poly[(2,2′-bithiophene)-alt-(4,7-bis((2-decyltetradecyl)thiophen-2-yl)-5,6-difluoro-2-propyl-2H-benzo[d][1,2,3]triazole)] (PT2-FTAZ), where the sulfur atoms in the benzothiadiazole moieties of PffBT4T-2OD are replaced with nitrogen atoms carrying a linear C₃H₇ side-chain; these polymers are mixed with the phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) acceptor. This study also discusses the nature of the charge-transfer electronic states appearing at the donor–acceptor interfaces, the electronic couplings relevant for the charge-recombination process, and the electron-transfer features between neighboring PC₇₁BM molecules.

Minor structural modifications to the polymer backbone can change substantially the blend morphology and thus device performance of a bulk-heterojunction solar cell. This computational work, based on a tight combination of molecular dynamics simulations and density functional theory calculations, elucidates the molecular-scale impact that the structural changes to the polymer backbone have on the “local” morphology of the mixed regions.

MXene, an important and increasingly popular category of postgraphene 2D nanomaterials, has been rigorously investigated since early 2011 because of advantages including flexible tunability in element composition, hydrophobicity, metallic nature, unique in-plane anisotropic structure, high charge-carrier mobility, tunable band gap, and favorable optical and mechanical properties. To fully exploit these potentials and further expand beyond the existing boundaries, novel functional nanostructures spanning monolayer, multilayer, nanoparticles, and composites have been developed by means of intercalation, delamination, functionalization, hybridization, among others. Undeniably, the cutting-edge developments and applications of clay-inspired 2D MXene platform as electrochemical electrode or photo-electrocatalyst have conferred superior performance and have made significant impact in the field of energy and advanced catalysis. This review provides an overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene and their hybrids, highlights the state-of-the-art progresses of MXene-based applications with respect to supercapacitors, batteries, electrocatalysis and photocatalysis, and presents the challenges and prospects in the burgeoning field.

An overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene, and their hybrids is provided in this review. The state-of-the-art progresses of MXene-based applications with respect to supercapacitors, batteries, electrocatalysis, and photocatalysis are highlighted, and the challenges and prospects in the burgeoning field of MXene are presented.

Significant development has been achieved in nonfullerene organic solar cells. However, most of the high-efficiency nonfullerene systems are composed of polymer donors and fused-ring acceptors, and only a few small molecule donors can work well. Herein, a new A–D–A small molecule donor named NDTSR with naphtho[1,2-b:5,6-b′]dithiophene (NDT) as building blocks is synthesized. Two energy levels well-matched fused-ring acceptors ITIC and IDIC are chosen to construct all-small-molecule solar cells with NDTSR, respectively. When mixed with IDIC, a high power conversion efficiency (PCE) of 8.05% is achieved, which is the highest efficiency for NDT-based small molecule donor. However, the NDTSR:ITIC system only exhibits a low PCE of 1.77%. The big difference in the performance of these two systems should be attributed to the different morphology and phase separation resulting from the crystallinity and aggregation ability of the acceptors. The results demonstrate that NDT-based small molecule is a promising candidate donor for all-small-molecule systems, while the crystallinity of fused-ring acceptors is a critical factor for optimizing the phase separation in the active layer.

An all-small-molecule nonfullerene solar cell is constructed with a novel small molecule NDTSR as donor, and ITIC and IDIC as acceptor, respectively. Through enhancing the crystallinity of acceptors, a high power conversion efficiency of 8.05% is obtained, which indicates that the crystallinity of the acceptor is a key factor for the performance of all-small-molecule solar cells.

Polymer aggregation plays a critical role in the miscibility of materials and the performance of all-polymer solar cells (APSCs). However, many aspects of how polymer texturing and aggregation affect photoactive blend film microstructure and photovoltaic performance are poorly understood. Here the effects of aggregation in donor–acceptor blends are studied, in which the number-average molecular weights (M_ns) of both an amorphous donor polymer, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) and a semicrystalline acceptor polymer, poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) are systematically varied. The photovoltaic performance is correlated with active layer microstructural and optoelectronic data acquired by in-depth transmission electron microscopy, grazing incidence wide-angle X-ray scattering, thermal analysis, and optical spectroscopic measurements. Coarse-grained modeling provides insight into the effects of polymer aggregation on the blend morphology. Notably, the computed average distance between the donor and the acceptor polymers correlates well with solar cell photovoltaic metrics such as short-circuit current density (J_sc) and represents a useful index for understanding/predicting active layer blend material intermixing trends. Importantly, these results demonstrate that for polymers with different texturing tendencies (amorphous/semicrystalline), the key for optimal APSC performance, photovoltaic blend morphology can be controlled via both donor and acceptor polymer aggregation.

The templating effects in morphology engineering by regulating aggregation are clearly demonstrated for the first time in all-polymer solar cells, where the morphology may be templated by the amorphous phase in one blend and by the semicrystalline phase in another, all dictated by the degree of polymer aggregation.

A major breakthrough in the field of organic photovoltaics (OPVs) was the development of the donor/acceptor heterojunction that aids in separating Coulombically bound excitons that are generated upon photoabsorption. Additionally, bound charge transfer (CT) states that result from the exchange of charge carriers across the donor/acceptor interface are believed to play an important role in charge generation. Though organic thin films are often disordered, enhancements to the local structural order at the donor/acceptor interface have recently been shown to greatly influence CT state energetics and the charge generation process. In this progress report, recent efforts to understand the role that donor/acceptor morphology plays in the behavior of CT states and the resulting implications on OPV function are presented. It is aimed to provide a survey of different experimental approaches and to present a balanced examination of current interpretations of key results, and to offer best practices for the fabrication and study of morphologically tunable donor/acceptor CT states.

The local morphology at organic donor/acceptor interfaces has recently been shown to greatly influence charge transfer state energies and dynamics. This progress report summarizes some of the key discussions in recent literature concerning the role of local morphology in the charge transfer and charge generation process in organic photovoltaics, as well as the potential impact on device performance.

Nonfullerene polymer solar cells (PSCs) are fabricated by using one wide bandgap donor PBDB-T and one ultranarrow bandgap acceptor IEICO-4F as the active layers. One medium bandgap donor PTB7-Th is selected as the third component due to the similar highest occupied molecular orbital level compared to that of PBDB-T and their complementary absorption spectra. The champion power conversion efficiency (PCE) of PSCs is increased from 10.25% to 11.62% via incorporating 20 wt% PTB7-Th in donors, with enhanced short-circuit current (J_SC) of 24.14 mA cm⁻² and fill factor (FF) of 65.03%. The 11.62% PCE should be the highest value for ternary nonfullerene PSCs. The main contribution of PTB7-Th can be summarized as the improved photon harvesting and enhanced exciton utilization of PBDB-T due to the efficient energy transfer from PBDB-T to PTB7-Th. Meanwhile, PTB7-Th can also act as a regulator to adjust PBDB-T molecular arrangement for optimizing charge transport, resulting in the enhanced FF of ternary PSCs. This experimental result may provide new insight for developing high-performance ternary nonfullerene PSCs by selecting two well-compatible donors with different bandgap and one ultranarrow bandgap acceptor.

Highly efficient ternary nonfullerene polymer solar cells (PSCs) are fabricated by employing two well-compatible donors with complementary absorption spectra and one ultranarrow bandgap acceptor. The power conversion efficiency and short-circuit current density of ternary PSCs are simultaneously increased to 11.62% and 24.14 mA cm⁻² by incorporating 20 wt% PTB7-Th due to the enhanced photon harvesting and optimized film morphology.

A terthieno[3,2-b]thiophene (6T) based fused-ring low bandgap electron acceptor, 6TIC, is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron-rich π-conjugated 6T core and reduced resonance stabilization energy. The rigid, π-conjugated 6T also offers lower reorganization energy to facilitate very low V_OC loss in the 6TIC system. The analysis of film morphology shows that PTB7-Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7-Th:6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high J_SC > 20 mA cm⁻² and a high V_OC of 0.83 V with a relatively low V_OC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7-Th:6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high J_SC is quite rare for organic solar cells.

Terthieno[3,2-b]thiophene (6T) based low bandgap fused-ring electron acceptor, 6TIC, is developed for highly efficient solar cells, which exhibits a high power conversion efficiency (PCE) of 11.07% with a high J_SC over 20 mA cm⁻² and a high V_OC of 0.83 V with a relatively low V_OC loss (≈0.55 V). Moreover, the semitransparent solar cell based on PTB7-Th:6TIC exhibits a very promising PCE of 7.62%.

Donor–acceptor (D-A) type π-conjugated copolymers with crystalline behavior have been extensively investigated as donor semiconductors in organic photovoltaics (OPVs). On the other hand, the development of high-performance amorphous donor materials is still behind. The amorphous donor copolymer DTS-C₀(F₂) consisting of dithieno[3,2-b:2′,3′-d]silole (DTS) donor unit and the recently developed fluorine-substituted naphtho[2,3-c]thiophene-4,9-dione (C₀(F₂)) acceptor unit shows moderate photovoltaic performance upon blending with PC₇₁BM. In this work, to enhance the hole-transporting characteristics, a 3-hexylthiophene (HT) spacer unit is integrated into the conjugated backbone, resulting in a new amorphous copolymer DTS-HT-C₀(F₂). The strong electron-accepting nature of C₀(F₂) allows the introduction of the HT spacer without affecting the frontier orbital energies and thus the D-A character. Without using solvent additives and thermal annealing, OPVs based on DTS-HT-C₀(F₂) and [6,6]-phenyl-C71-butyric acid methyl ester PC₇₁BM show an improved power conversion efficiency of 9.12%. Investigation of the device physics unambiguously reveals that the hole mobility of the copolymer in the blend is increased by an order of magnitude by the introduction of HT, while keeping an amorphous film nature, leading to higher short-circuit current density and fill factor. These results demonstrate the realization of high-performance OPVs based on amorphous active layers.

Donor–acceptor type π-conjugated copolymer based on fluorine-substituted naphtho[2,3-c]thiophene-4,9-dione is developed for an amorphous donor material in organic photovoltaics. Bulk-heterojunction solar cells using the blend film of synthesized copolymer and PC₇₁BM as an acceptor show photovoltaic characteristics with power conversion efficiencies of 9.12%. Blend-film investigation reveals that this high performance comes from the increased hole-transporting nature of the copolymer.

In this work, four donor (D)–acceptor (A) copolymers based on benzodithiophene (BDT) and benzothiadiazole (BT) with different alkylthiolated and/or fluorinated side chains are developed for efficient fullerene and nonfullerene polymer solar cells (PSCs). The synergistic effect of sulfuration and fluorination on the optical absorption, energy level, crystallinity, carrier mobility, blend morphology, and photovoltaic performance is investigated systematically. By incorporating sulfur atoms onto the side chains, a little blueshifted but significantly increased absorption can be obtained for PBDTS-FBT compared to PBDT-FBT. On the other side, a little more blueshifted but much stronger absorption and much lower-lying highest occupied molecular orbital (HOMO) level can be realized for PBDTF-FBT when introducing fluorine atoms instead of sulfur atoms. With the combination of both fluorination and sulfuration strategies, PBDTS-FBT exhibits the best absorption ability, lowest HOMO energy level, and highest crystallinity, which make PBDTSF-FBT devices show the highest power conversion efficiency (PCE) of 10.69% in fullerene PSCs and 11.66% in nonfullerene PSCs. The PCE of 11.66% is the best value for PSCs based on BT-containing copolymer donors reported so far. The results indicate that fluorination and sulfuration have a synergistically positive effect on the performance of D–A photovoltaic copolymers and their solar cell devices.

With the combination of fluorination and sulfuration strategies, new benzodithiophene (BDT)–benzothiadiazole (BT) copolymer donors are developed for improving the optical absorption, energy level, carrier mobility, and blend morphology. The fabricated fullerene and nonfullerene polymer solar cells exhibit high power conversion efficiencies of 10.69% and 11.66%.

In this work, sidechain engineering on conjugated fused-ring acceptors for conformation locking is demonstrated as an effective molecular design strategy for high-performance nonfullerene organic solar cells (OSCs). A novel nonfullerene acceptor (ITC6-IC) is designed and developed by introducing long alkyl chains into the terminal electron-donating building blocks. ITC6-IC has achieved definite conformation with a planar structure and better solubility in common organic solvents. The weak electron-donating hexyl upshifts the lowest unoccupied molecular orbital level of ITC6-IC, resulting in a higher V_OC in comparison to the widely used ITIC. The OSCs based on PBDB-T:ITC6-IC reveal a promising power conversion efficiency of 11.61% and an expected high V_OC of 0.97 V. The weaker π–π stacking induced by steric hindrance affords ITC6-IC with enhanced compatibility with polymer donors. The blend film treated with suitable thermal annealing exhibits a fibril crystallization feature with a good bicontinuous network morphology. The results indicate that the molecular design approach of ITC6-IC can be inspirational for future development of nonfullerene acceptors for high efficiency OSCs.

Conformation locking by introducing alkyl chains onto central electron-donating building blocks has been explored on fused-ring electron acceptor for high-performance nonfullerene organic solar cells. PBDB-T:ITC6-IC based devices treated with suitable thermal annealing reveal a promising power conversion efficiency of 11.61% and an expected high V_OC of 0.97 V with a small energy loss.

To achieve high-performance large-area flexible polymer solar cells (PSCs), one of the challenges is to develop new interface materials that possess a thermal-annealing-free process and thickness-insensitive photovoltaic properties. Here, an n-type self-doping fullerene electrolyte, named PCBB-3N-3I, is developed as electron transporting layer (ETL) for the application in PSCs. PCBB-3N-3I ETL can be processed at room temperature, and shows excellent orthogonal solvent processability, substantially improved conductivity, and appropriate energy levels. PCBB-3N-3I ETL also functions as light-harvesting acceptor in a bilayer solar cell, contributing to the overall device performance. As a result, the PCBB-3N-3I ETL-based inverted PSCs with a PTB7-Th:PC₇₁BM photoactive layer demonstrate an enhanced power conversion efficiency (PCE) of 10.62% for rigid and 10.04% for flexible devices. Moreover, the device avoids a thermal annealing process and the photovoltaic properties are insensitive to the thickness of PCBB-3N-3I ETL, yielding a PCE of 9.32% for the device with thick PCBB-3N-3I ETL (61 nm). To the best of one's knowledge, the above performance yields the highest efficiencies for the flexible PSCs and thick ETL-based PSCs reported so far. Importantly, the flexible PSCs with PCBB-3N-3I ETL also show robust bending durability that could pave the way for the future development of high-performance flexible solar cells.

An n-type doping fullerene electrolyte (PCBB-3N-3I) with high-content doping groups, resulting in high conductivity and well-matched energy levels, is synthesized. The inverted polymer solar cells with PCBB-3N-3I electron transport layer show a record efficiency in the flexible polymer solar cells with an extremely high bending durability and thickness-insensitive photovoltaic behavior.

Molecular engineering of nonfullerene acceptors (NFAs) plays a vital role in the development of organic photovoltaics. Oxygen as an electron donating atom is incorporated into the NFA system as alkoxyl forms at central, terminal, or central conjugated moieties due to the tunability at structural conformation, solubility, electron donating ability, absorption, energy levels, etc. In this work, a novel dipyran-based ladder-type building block (Ph-DTDP), which possesses two oxygen atoms in the conjugated skeleton, is designed and facilely synthesized. It is applied as the donor core for the acceptor–donor–acceptor-type NFA design and such functionalized-O efficiently enhances the electron donating ability, lowers the band gap, redshifts and extends the absorption spectra. In addition, the π-bridge effects are considered as well. Photovoltaic performances are systematically investigated and a high power conversion efficiency of 9.21% can be afforded with an energy loss of 0.57 eV. Meanwhile, the morphologies as well as the carrier mobilities of the blend films are studied to assist further understanding of the structure–property relationships. Overall, the study in this work provides a new promising ladder-type dipyran building block and brings in a novel way to use oxygen in NFA molecular structure design.

Dipyran-based ladder-type building block (Ph-DTDP), which possesses two oxygen atoms in the conjugated skeleton and four flanking hexylphenyl side chains, is facilely synthesized. The corresponding acceptor–donor–acceptor-type nonfullerene acceptors are prepared and the influences of O-functionalization and π-bridges on energy levels, absorption spectra, crystalinity, morphologies, and photovoltaic performances are systematically studied.

Organic solar cells (OSCs) based on bulk heterojunction structures are promising candidates for next-generation solar cells. However, the narrow absorption bandwidth of organic semiconductors is a critical issue resulting in insufficient usage of the energy from the solar spectrum, and as a result, it hinders performance. Devices based on multiple-donor or multiple-acceptor components with complementary absorption spectra provide a solution to address this issue. OSCs based on multiple-donor or multiple-acceptor systems have achieved power conversion efficiencies over 12%. Moreover, the introduction of an additional component can further facilitate charge transfer and reduce charge recombination through cascade energy structure and optimized morphology. This progress report provides an overview of the recent progress in OSCs based on multiple-donor (polymer/polymer, polymer/dye, and polymer/small molecule) or multiple-acceptor (fullerene/fullerene, fullerene/nonfullerene, and nonfullerene/nonfullerene) components.

This progress report provides an overview of the most impactful recent progress in high-performance organic solar cells based on multiple-donor (polymer/polymer, polymer/dye, and polymer/small molecule) or multiple-acceptor (fullerene/fullerene, fullerene/nonfullerene, and nonfullerene/nonfullerene) components, focusing particularly on the interactions between different components from the perspective of morphology and photophysics.

A novel small molecule acceptor MeIC with a methylated end-capping group is developed. Compared to unmethylated counterparts (ITCPTC), MeIC exhibits a higher lowest unoccupied molecular orbital (LUMO) level value, tighter molecular packing, better crystallites quality, and stronger absorption in the range of 520–740 nm. The MeIC-based polymer solar cells (PSCs) with J71 as donor, achieve high power conversion efficiency (PCE), up to 12.54% with a short-circuit current (J_SC) of 18.41 mA cm⁻², significantly higher than that of the device based on J71:ITCPTC (11.63% with a J_SC of 17.52 mA cm⁻²). The higher J_SC of the PSC based on J71:MeIC can be attributed to more balanced μ_h/μ_e, higher charge dissociation and charge collection efficiency, better molecular packing, and more proper phase separation features as indicated by grazing incident X-ray diffraction and resonant soft X-ray scattering results. It is worth mentioning that the as-cast PSCs based on MeIC also yield a high PCE of 11.26%, which is among the highest value for the as-cast nonfullerene PSCs so far. Such a small modification that leads to so significant an improvement of the photovoltaic performance is a quite exciting finding, shining a light on the molecular design of the nonfullerene acceptors.

A novel small-molecule acceptor MeIC with a methylated end-capping group is developed. Compared to unmethylated counterparts (ITCPTC), MeIC exhibits higher lowest unoccupied molecular orbital (LUMO) level, tighter molecular packing, and better crystallite quality. MeIC-based polymer solar cells with J71 as donor achieve high power conversion efficiency up to 12.54%, significantly higher than that of the device of ITCPTC.

A fused tris(thienothiophene) (3TT) building block is designed and synthesized with strong electron-donating and molecular packing properties, where three thienothiophene units are condensed with two cyclopentadienyl rings. Based on 3TT, a fused octacylic electron acceptor (FOIC) is designed and synthesized, using strong electron-withdrawing 2-(5/6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile as end groups. FOIC exhibits absorption in 600–950 nm region peaked at 836 nm with extinction coefficient of up to 2 × 10⁵m^–1 cm^–1, low bandgap of 1.32 eV, and high electron mobility of 1.2 × 10^–3 cm² V^–1 s^–1. Compared with its counterpart ITIC3 based on indacenothienothiophene core, FOIC exhibits significantly upshifted highest occupied molecular orbital level, slightly downshifted lowest unoccupied molecular orbital level, significantly redshifted absorption, and higher mobility. The as-cast organic solar cells (OSCs) based on blends of PTB7-Th donor and FOIC acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 12.0%, which is much higher than that of PTB7-Th: ITIC3 (8.09%). The as-cast semitransparent OSCs based on the same blends show PCEs of up to 10.3% with an average visible transmittance of 37.4%.

A fused tris(thienothiophene)-based electron acceptor with strong near-infrared absorption and high electron mobility is designed, synthesized, and applied in as-cast organic solar cells and as-cast semitransparent organic solar cells, which exhibit efficiencies of 12.0% and 10.3%, respectively.