Interface Engineering of Perovskite Solar Cells with Air Plasma Treatment for Improved Performance

For high-efficiency perovskite solar cells (PSCs), interface engineering becomes critical for carrier collection from the active perovskite material to the transport layer. To enhance the power conversion efficiency (PCE), herein we demonstrate a novel method named surface plasma treatment on a mesoporous TiO2 electron-transport layer (ETL) to improve electron extraction and transport properties at the perovskite/TiO2 interface. According to the XPS results, the plasma treatment induced a partial reduction of Ti4+ to Ti3+ within the TiO2 lattice and increased the concentration of oxygen vacancies on the TiO2 surface. Ultraviolet photoelectron spectra (UPS) show that the Fermi level of TiO2 upshifts about 0.2 eV which may effectively promote carrier separation and transfer at the perovskite/TiO2 interface. In addition, these created donor levels of Ti3+ and oxygen vacancies donate extra electrons, increasing the conductivities of TiO2 films and which could further promote transport. The time-resolved photoluminescence spectra (TRPL) confirm that the decay time decreases dramatically from 656 ns to 235 ns after 90 s plasma treatment, which indicates a more efficient electron-transfer process. Based on all the above-mentioned results, a remarkable enhancement in cell efficiency was obtained, such that the average efficiency was improved from 11.5 % to 14.3 % under AM 1.5G irradiation (100 mW cm-2 ).