An Analytical Approach to CH3NH3PbI3 Perovskite Solar Cells Based on Different Hole Transport Materials

Organic halide perovskite solar cells (PSC's) have achieved high efficiencies in a relatively short amount of time. In order to attain efficiency in the neighborhood of the Shockley-Queisser (SQ) limit, additional modifications are continuously being made. A simple lumped circuit model, which had been previously used to investigate organic and inorganic thin-film solar cells, is used in this study to gain more insight into the effects of these modifications on the performance-related factors. It is examined that the changes in the lumped-circuit parameters associated with the device performances when different hole transport materials (HTM's) such as PEDOT:PSS, NiOx, and PTAA or when different underneath substrates are employed. The reason for this interest is the well-accepted fact that the defect formation greatly hinders the formation of photo-generated charge carriers. Using the time-resolved surface photovoltage measurements, we show that the photo-induced charge separation and charge migration are greatly influenced by the HTM's. The resulting changes were analyzed in detail. Unlike what occurs when CH3NH3PbI3 is deposited onto bare ITO or PEDOT:PSS, the long-lived (from micro-millisecond) charge separations are observed when the NiOx is used as the HTL. These observations point to the need to examine other low-cost HLM's or combinations of them, for use to improve the solar energy conversion efficiencies of the PSC's.