Valence state regulated SnOx bottom and top contacts for inverted perovskite solar cells

Interfacial recombination and the stability of contact materials limit the performance of inverted perovskite solar cells (PSCs). Here, iodine vapor treatment is used to regulate the oxidation state of SnOx for two different contact functions. Increasing the treatment duration decreases the fitted Sn2+/Sn4+ area ratio and changes the XPS-estimated nominal composition from SnO1.09 to SnO1.91. The optical gap increases from approximately 3.75 to 4.11 eV, accompanied by changes in the oxygen environments and vacuum-referenced energy levels. The 10 min SnO1.25 film replaces PEDOT:PSS at the bottom hole-collection contact, while the 30 min SnO1.91 film replaces bathocuproine as a buffer at the PCBM/Ag electron contact. Combining the two substitutions increases the power conversion efficiency from 14.44% to 17.80%, with a small difference between forward and reverse scans. After 1000 h of ambient storage, the unencapsulated device retains approximately 77% of its initial efficiency, compared with approximately 50% for the reference. The results demonstrate the use of oxidation-state-regulated SnOx at the bottom and top contacts in inverted PSCs.