Limiting factors for the power conversion efficiency of hybrid organic-inorganic halide perovskite photovoltaic devices under operating conditions.*

We use first-principles calculations and thermodynamic modelling to establish that the theoretical maximum efficiency limit is in the range of ~25-27\% under operating conditions. We examine compounds of ABX3 composition, where A={Methylammonium, Methyleniminium, Formamidinium, Guanidinium}, B={Pb,Sn}, X={Br,I} with estimated band-gaps of 0.9 to 2.3 eV. Effective band masses and level alignments for all compounds are determined. Based on this data we setup an effective circuit model for a PIN-cell, including entropic contributions to the free energy of the carriers. Our results indicate that the state-of-the art perovskite based solar cells, due to their intrinsic resilience to defect-induced trap-states and interface quality is already above 80\% of their theoretical maximum efficiency. Our result provide a useful framework for estimating the impact of level alignment to hole and electron transporting materials on the PCE. It also indicates the need for the use of multi-junction cells or hot-carrier extraction in order to reach cells of more than ~27\% power conversion efficiency at room temperature. \footnote{O. Gr\aa n\"as \emph{et al.} Sci. Rep. 6, 36108; doi: 10.1038/srep36108 (2016)}