Electrical loss management by molecularly manipulating dopant-free poly(3-hexylthiophene) towards 16.93 % CsPbI${}_2$Br solar cells

Inorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture-induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant-free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3-hexylthiophene) with a small molecule, i.e., SMe-TATPyr. The developed P3HT/SMe-TATPyr HTL shows a three-time increase of carrier mobility owing to breaking the long-range ordering of "edge-on'' P3HT and inducing the formation of "face-on'' clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI${}_2$Br perovskite solar cell demonstrates a record-high efficiency of 16.93 % for dopant-free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low-humidity condition (10-25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours. (© 2021 Wiley‐VCH GmbH)