We present a non-fullerene electron acceptor bearing a fused 10-heterocyclic ring with a narrow band gap, which achieved a power conversion efficiency of 6.5% when paired with PTB7-Th.

Semi-transparent perovskite solar cells (Pero-SCs) are realized by tuning the band gap of the perovskite to resolve the trade-off between the transparency and efficiency of the photo-absorber. We synthesized wide-bandgap MAPbI_3−xBr_x perovskite, and the transparency and efficiency of the corresponding semi-transparent Pero-SCs were investigated systematically by varying the I : Br ratio and thickness of the perovskite film. Increasing Br content widened the bandgap of perovskite (i.e., blue shift of the absorption edge), and led to an increase in the average visible transmittance (AVT). This strategy allowed for high AVTs, and concomitantly achieved high power conversion efficiencies. Meanwhile, increasing the Br content could facilitate formation of perovskite films with large grains that were highly crystallized. Compared with the narrow-bandgap perovskite, the wide-bandgap perovskite showed advantages for obtaining semi-transparent Pero-SCs with thick perovskite films (>200 nm) and high (20%) transparency.