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High open‐circuit voltage (Voc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non‐fused ring electron acceptors (NFREAs), HF‐BTA33 and HCl‐BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron‐phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF‐BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a Voc of 1.232 V, higher than that of symmetric analogue F‐BTA33 (PCE=10.02 %, Voc=1.197 V). Notably, PTQ10 : HCl‐BTA33 achieves the highest PCE of 12.54 % with a Voc of 1.201 V due to the long‐range ordered π–π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and Voc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs. [ABSTRACT FROM AUTHOR]

In recent years, the organic solar cells (OSCs) research hotspot is the modification of end groups and alkyl side chains of A‐DA'D‐A‐type nonfullerene acceptors (NFAs). However, the development of novel NFAs by changing the different bridged atom substitution of the central core is lagging behind. Herein, two wide‐bandgap A2‐A1‐D‐A1‐A2‐type NFAs with different central cores, namely BTA501 and BTA502, are developed to improve the photovoltaic performance of high‐voltage OSCs. BTA501 adopted an indacenodithiophene (IDT) core, whereas BTA502 applied a silaindacenodithiophene (SiIDT) core. Expectedly, the SiIDT‐based BTA502 exhibits a higher lowest unoccupied molecular orbital level and wider bandgap than BTA501, which thus enhances the open‐circuit voltage (VOC) but slightly decreases the short‐circuit current density (JSC) of OSCs. Moreover, the stronger self‐aggregation characteristics and weaker π–π stacking of BTA502 severely affect the exciton dissociation and charge transport. When blended with two classic p‐type polymers J52‐F and PTB7‐Th, both combinations based on BTA502 exhibit inferior device performance compared with BTA501. Excitingly, the device of J52‐F: BTA501 achieves a VOC of 1.037 V with a power conversion efficiency of 11.82% and a JSC of 15.89 mA cm−2, which are among the highest values for high‐voltage OSCs with VOC above 1.0 V. [ABSTRACT FROM AUTHOR]

Rational design and synthesis of high-performance doping-free hole transport polymers is critical to achieve high-efficiency and stable perovskite solar cells (PSCs). Side chain engineering is a widely employed strategy for modulating the photoelectronic properties of polymers. In this study, based on dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophenes (DTBDT) as D unit, benzo[ d ][1,2,3]triazole (BTA) as A segment, and thiophene as a π bridge, three D-π-A type polymeric materials with different length of alkyl side chain (PE51, PE52, and PE53) were utilized as hole transport materials in CsPbI 2 Br-based PSCs and perovskite/organic tandem solar cells (TSCs). With the increase of alkyl chain length from 2-butyloctyl (PE51) to 2-hexyldecyl (PE52) and to 2-octyldodecyl (PE53), the highest occupied molecular orbital energy level of the polymer gradually decreases, and the molecular stacking of the material gradually shifts from edge-on stacking to face-on stacking. Moreover, among three polymers, the PE53 exhibits the most efficient hole extraction at the CsPbI 2 Br/hole transport layer (HTL) interface. Hence, the CsPbI 2 Br-based PSCs and perovskite/organic TSCs employing PE53 as HTL realize the highest power conversion efficiency (PCE) of 17.65% and 23.07%, respectively. Our results indicate that side chain engineering of HTM is an effective strategy to modulate their molecular orientation and improve the photovoltaic performance of PSCs. [Display omitted] • The polymers PE51-53 with different length of alkyl side chain were used as hole transport layers for CsPbI 2 Br-based PSCs and TSCs. • The champion PCE of single-junction CsPbI 2 Br PSCs arrived 17.65%, with high V OC of 1.42 V. • The monolithic CsPbI 2 Br/D18:Y6 TSCs with PE53 based inter-connecting layer achieved the highest PCE of 23.07%. [ABSTRACT FROM AUTHOR]