Evolution of the Electronic Traps in Perovskite Photovoltaics during 1000 h at 85 °c

With growing demands on the stability of perovskite photovoltaics against various degradation factors, understanding and controlling the defect characteristics of devices have become the most essential issues to be resolved. In this work, the organometal halide perovskite is modified with a lithium-fluoride ionic passivator that enables highly stable and efficient solar cells with a power-conversion efficiency of over 21%, retaining up to ∼90% after 1000 h at 85 °C. The thermal degradation regressions of the films and devices have been temporally investigated, and the trap density of states has been scrutinized as a function of time. Surprisingly, the electronic traps of the solar cells exhibit exponential relaxations in both the trap densities and energy levels as thermally stressed, and the incorporation of LiF has greatly enhanced this relaxation with the mitigation of the following degradation. It is suggested that LiF not only passivates the initial formation of the traps but also controls their roles and behaviors under the thermal degradation of devices.