Photoluminescence kinetics for monitoring photoinduced processes in perovskite solar cells

The research on halide perovskites is in its peak activity at the moment due to the materials potential application in photovoltaics. It is well known that slow processes, from seconds to minutes, are very significant in perovskite films and devices as compared to conventional photovoltaic materials. The kinetics of photoluminescence (PL) is informative data for studying such processes. In particular, tracing the change in PL intensity under continuous laser excitation provides information on charge carriers recombination and the efficiency of their extraction from the absorber layer. Although widely available, this method was applied mainly for the research on thin films. However, monitoring PL kinetics on complete solar cells as well as on incomplete device stacks at each fabrication and lifespan stage can provide an important information on the device optimization and determination of the layers and interfaces that limit device efficiency and stability. Here, we demonstrate the advantages of the method by tracing the evolution of PL kinetics at seconds-to-minutes timescale upon: (1) varying perovskite composition (MAPbI(3), Cs(0.15)FA(0.85)PbI(2.7)Br(0.3), Cs-0.05(MA(0.15)FA(0.85))(0.95)PbI2.55Br0.45); (2) layer-by-layer stack construction of Cs(0.15)FA(0.85)PbI(2.7)Br(0.3)-based solar cell and (3) the device on-shelf degradation. In this way, information on charge carrier recombination, diffusion and extraction is revealed purely by optical, contactless and non-destructive means.