A nanomaterial-regulated oxidation of hole transporting layer for highly stable and efficient perovskite solar cells

Small molecule 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD) is widely used as a hole transport material for efficient perovskite solar cells (PSCs). However, the conventional doping of spiro-OMeTAD with hygroscopic lithium salt and volatile 4-tert-butylpyridine is a time-consuming process and also leads to a poor device stability, which significantly hinder the commercialization of PSCs. Here, we develop a nanomaterial-regulated doping strategy to pre-oxidize spiro-OMeTAD into radicals in the precursor solution with tin sulfoxide (SnSO) nanomaterials prepared at high temperature. Due to the greater Gibbs free energy change of the Li2SnO3 formation reaction than that of the reaction of O2 molecules with Li+ ions, the generated Li2SnO3 not only inhibits the aggregation of Li-TFSI, but also accelerates the oxidation of spiro-OMeTAD HTM by rapidly producing sufficient spiro-OMeTAD•+TFSI– radicals. Furthermore, SnSO improves the energy level arrangement between perovskite film and hole transport layer (HTL), reduces interfacial defects, and improves carrier transport, morphology and conductivity in HTL by inhibiting ion aggregation and migration. Based on this new strategy, a high-power conversion efficiency higher than 24% and a greatly improved stability are achieved in PSCs under the harsh conditions of a high temperature and a high humidity, which provides a practical strategy for further commercialization of stable and efficient PSCs.