It is worth noting that active layer materials play fundamental roles in boosting the efficiency of an OSC. Indeed, the development of non-fullerene acceptors (NFAs) has led to continuous improvements in the performance of OSCs over the past 5 years. [6][7][8] Furthermore, among the various types of active layer materials, molecules with acceptor-donor-acceptor (A-D-A) architectures have demonstrated excellent properties, including enhanced intramolecular charge transfer (ICT), tunable absorption ranges, and ordered molecular packing orientations. [9][10][11] Presently, polymer-based OSCs have rapidly developed, with power conversion efficiencies (PCEs) exceeding 19%, which is mainly attributable to the invention of new acceptors, especially A-D-A type acceptors, such as ITIC, [12] Y6, and their derivatives. [13] However, polymer-based OSCs suffer from batch-to-batch reproducibility issues and are hard to further purify. In contrast, all-small-molecule OSCs (ASM-OSCs) have well-defined chemical structures and exhibit few batch-tobatch variations. [14][15][16][17] The fullerene era saw the development of ASM-OSCs with efficiencies comparable to their polymer counterparts. For example, our group designed a series of A-D-Atype oligothiophene (OT) small-molecule donors that delivered efficiencies of more than 10% in DRCN5T:PC 71 BM-based ASM-OSC, which was the highest efficiency reported in the OSC community in 2015. [18] We subsequently constructed a tandem OSC using two SM donors with complementary absorption profiles (DR3TSBDT and DPPEZnP-TBO) as donors and PCBM as the acceptor in the front and rear subcells, [19] which delivered a record PCE of 12.7% following device optimization. The past five years has seen increasing levels of attention paid to ASM-OSCs that incorporate NFAs, owing to the rapid development of NFAs; such OSCs have also demonstrated great potential. However, the PCEs of NFA-based ASM-OSCs (>9%) [20,21] lagged behind those of polymer-based OSCs (>13%) [22][23][24] before 2017, which was mainly due to the lack of suitable active layer material systems. The advent of ITIC, Y6, and their derivatives as A-D-A-type acceptors saw exciting advancements in ASM-OSCs owing to continuous NFA and SM-donor innovations. ASM-OSCs are currently able to deliver PCEs of 9-17% through careful donor and acceptor material design and morphology control, [25][26][27] which has narrowed the efficiency gap with their polymer-based OSC counterparts.In this review, we summarize recent progress in ASM-OSCs by mainly focusing on efficient SM-donor and NFA innovations, as well as relationships between molecular structure, Active layer material plays a critical role in promoting the performance of an organic solar cell (OSC). Small-molecule (SM) materials have the merits of well-defined chemical structures, few batch-to-batch variations, facile synthesis and purification procedures, and easily tuned properties. SMdonor and non-fullerene acceptor (NFA) innovations have recently produced all-small-molecule (ASM) devices with pow...

The recent progress in non-fused ring electron acceptor-based organic solar cells has been reviewed from the perspective of material design strategies.

Organic solar cells (OSCs) with thick active layers exhibit great potential for future roll‐to‐roll mass production. However, increasing the thickness of the active layer generally leads to unfavorable morphology, which decreases the device's performance. Therefore, it is a critical challenge to achieve OSCs with high efficiency and thick film simultaneously. Herein, a small molecular donor, ZW1, incorporating a bithiazole unit along with a thiophene group as a π‐bridge is reported. ZW1 with high crystallinity is employed to fabricate D18:ZW1:Y6 ternary devices, which enhances the crystallization, optimizes the morphology, and suppresses bimolecular recombination. Additionally, ZW1 shows better miscibility with D18, resulting in the preferred vertical phase distribution. As a result, an outstanding power conversion efficiency (PCE) of 18.50% is realized in ternary OSCs with 120 nm active layer thickness. Importantly, the thick ternary OSCs attain a high PCE of 16.67% (thickness ≈300 nm), significantly higher than the corresponding binary devices (13.50%). The PCE of 16.67% is one of the highest values for thick‐film OSCs reported to date. This work demonstrates that the incorporation of highly crystalline small‐molecule donors into ternary OSCs, possessing good miscibility with host materials, presents an effective strategy for fabricating highly efficient thick OSCs.

Comprehensive Summary All‐small‐molecule organic solar cells (ASM OSCs) are promising for commercial application due to the well‐defined chemical structures, convenient purifying process and low batch‐to‐batch variation. However, the similarity of molecule structures between small molecule donors and acceptors makes a hard regulation of their blend morphology, which will limit the efficiency. One of the efficient approaches is structural tuning, among which the π‐bridge engineering is considered as a good method to improve the blend morphology. Herein, we synthesized two porphyrin‐based small‐molecule donors, Por‐BR and Por‐TR, by introducing alkoxybenzene and alkylthiophene as π bridges. The Por‐BR‐based active layer produces poor morphology and does not achieve satisfying device efficiency because of the excessive aggregation tendency. As for Por‐TR, an efficiency of 11.26% is achieved with such a high open circuit voltage of 0.904 V. This study shows that altering π‐bridge units can facilitate the improvement of film morphology, finally increase the device performance, and also provides a sample for molecule designing in terms of structure‐property correlation.