Electroluminescence transients and correlation with steady-state solar output in solution-prepared CH3NH3PbI3 perovskite solar cells using different contact materials

Abstract

Electroluminescence (EL) transients of solution-prepared CH3NH3PbI3 perovskite solar cells were recorded under different biasing voltage conditions. The EL transients are reversible and show a sharp increase and a peak in the range of 1 s to 10 s, while after the peak the signal decays in 30 s to 60 s. The possible origins of the different features are discussed, pointing to a shift in the region of dominating recombination during biasing, governing the EL increase, and the creation of ion migration-induced non-radiative recombination centers during the EL decrease. Moreover, when ramping up the polarization voltage, the EL transients shorten, suggesting an acceleration of the microscopic mechanism with increasing electric fields. Cells prepared with compact instead of mesoporous TiO2 electron contact show faster dynamics, highlighting the link between dynamics and interface properties. Furthermore, experiments using cells with different hole contacts show that the observed behavior and the duration of the transient is similar in cells using Spiro-OmeTAD and copper phatlocyanine (CuPc). When considering the steady-state EL, the open circuit voltage under solar operation correlates with EL across samples with different HTL materials. A non-monotonous behavior is also observed in temperature-dependent EL transients, where maxima in EL as well as in time to the peak are observed around 30 °C, which is close to the temperature of crystalline phase change from tetragonal to cubic phase known in CH3NH3PbI3 at 37 °C.