Tailoring the molecular size of alkylamine modifiers for fabricating efficient and stable inverted CsPbI3 perovskite solar cells

An inorganic perovskite CsPbI3 with a suitable bandgap and excellent optoelectronic properties has attracted tremendous attention as a promising absorber in perovskite solar cells (PSCs). A surface modification strategy of introducing organic molecules with functional groups to treat perovskite films has been proven to be an effective route to achieve high-performance PSC devices. However, the effect of the molecular size of modifiers is almost ignored in surface passivation studies. In this work, three alkylamine modifiers with different molecular sizes were incorporated to post-treat CsPbI3 films to systematically investigate the influence of alkyl chain length on device performance. It was found that the alkylamine treatments can remarkably ameliorate film morphology and interface contact, passivate defects, and increase hydrophobicity, resulting in greatly improved device efficiency and stability. In particular, the CsPbI3 film treated with 1,5-pentanediamine (PDA) with a suitable chain length acquires optimum results owing to its most efficient passivation effect and suppressed nonradiative recombination. Consequently, the inverted PDA-based CsPbI3 PSC exhibits a champion power conversion efficiency (PCE) of 19.52%, outperforming the control device with a PCE of 13.43% and other alkylamine-treated devices. Furthermore, both the unencapsulated PDA-treated CsPbI3 films and PSC devices present considerably enhanced long-term stability. This work highlights the great significance of tailoring the molecular size of interfacial modifiers towards achieving efficient and stable inorganic PSCs.