Antimony‐based perovskite‐inspired materials (PIMs) are solution‐processable halide absorbers with interesting optoelectronic properties, low toxicity, and good intrinsic stability. Their bandgaps around 2 eV make them particularly suited for indoor photovoltaics (IPVs). Yet, so far only the fully inorganic Cs3Sb2ClxI9−x composition has been employed as a light‐harvesting layer in IPVs. Herein, the first triple‐cation Sb‐based PIM (CsMAFA‐Sb) in which the A‐site of the A3Sb2X9 structure consists of inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations is introduced. Simultaneously, the X‐site is tuned to guarantee a 2D structure while keeping the bandgap nearly unchanged. The presence of three A‐site cations is essential to reduce the trap‐assisted recombination pathways and achieve high performance in both outdoor and indoor photovoltaics. The external quantum efficiency peak of 77% and the indoor power conversion efficiency of 6.4% are the highest values ever reported for pnictohalide‐based photovoltaics. Upon doping of the P3HT hole‐transport layer with F4‐TCNQ, the power conversion efficiency of CsMAFA‐Sb devices is fully retained compared to the initial value after nearly 150 days of storage in dry air. This work provides an effective compositional strategy to inspire new perspectives in the PIM design for IPVs with competitive performance and air stability.

In this work, we introduce P3HT (poly(3-hexylthiophene-2,5-diyl)) as an efficient hole transport material (HTM) for lead-free Cs3Sb2I9 perovskite-inspired solar cells.

The design and synthesis of three star‐shaped nonfullerene (NFA) acceptors, TPA‐2T‐INCN, TPA‐2T‐BAB, and TPA‐T‐INCN, based on a triphenylamine (TPA) core and linked through π‐conjugated thiophene (T) spacers to different terminal units (3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile, INCN, and 1,3‐dimethylbarbituric acid, BAB), are reported. These materials are blended with the widely used poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) donor polymer and tested in flexible organic photovoltaics (OPVs). The NFAs capped with the strong electron‐withdrawing INCN unit perform best in OPVs. Both P3HT:TPA‐T‐INCN and P3HT:TPA‐2T‐INCN blends also show the highest photoluminescence quenching efficiency (95.8% and 92.6%, respectively). Surprisingly, when reducing the number of T spacers from 2 to 1, the solubility of the NFAs in o‐dichlorobenzene increases, leading to easier processing during the OPV fabrication and better surface morphology. This explains the best performance of TPA‐T‐INCN‐based blends in OPVs, with a champion power conversion efficiency of 1.13%.