Dopant-Free Polymer Hole Transport Materials for Highly Stable and Efficient CsPbI Perovskite Solar Cells.

All-inorganic perovskite CsPbI contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N for 3000 h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.