Dopant‐Free Polymer HTM‐Based CsPbI2Br Solar Cells with Efficiency Over 17% in Sunlight and 34% in Indoor Light

Abstract To abate the issue of moisture‐assisted phase transition of CsPbI 2 Br, caused by hygroscopic dopants used in the hole‐transporting material (HTM), developing dopant‐free HTMs is necessary. In this work, a new polymer, PDTDT, is developed as a dopant‐free HTM for CsPbI 2 Br solar cells, and the device performance and stability are systematically compared with cells employing dopant‐free P3HT. CsPbI 2 Br solar cells using PDTDT show an efficiency of 17.36% with V OC of 1.42 V and FF of 81.29%, which is one of the highest values for CsPbI 2 Br cells. Moreover, a record‐high efficiency of 34.20% with V OC of 1.14 V under 200 lux indoor light illumination and efficiency of 14.54% (certified efficiency of 13.86%) for a 1 cm 2 device under one sun are accomplished. Importantly, PDTDT shows superior/comparable device stability to P3HT, promising its potential to be an alternative to popular doped Spiro‐OMeTAD and P3HT HTM.