Pitfalls and prospects of optical spectroscopy to characterize perovskite-transport layer interfaces

Perovskite photovoltaics has witnessed an unprecedented increase in power conversion efficiency over the last decade. The choice oftransport layers, through which photo-generated electrons and holes are transported to electrodes, is a crucial factor for further improvingboth the device performance and stability. In this perspective, we critically examine the application of optical spectroscopy to characterizethe quality of the transport layer-perovskite interface. We highlight the power of complementary studies that use both continuous wave andtime-resolved photoluminescence to understand non-radiative losses and additional transient spectroscopies for characterizing the potentialfor loss-less carrier extraction at the solar cell interfaces. Based on this discussion, we make recommendations on how to extrapolate resultsfrom optical measurements to assess the quality of a transport layer and its impact on solar cell efficiency.