A phenomenological figure of merit for photovoltaic materials

Abstract

I derive a figure of merit (FOM) ΓPV to estimate the maximum efficiency attainable by a generic non-ideal photovoltaic (PV) absorber in a planar single-junction solar cell. This efficiency limit complements the more idealized limits derived from fundamental physics, such as the Shockley–Queisser (SQ) limit and its subsequent generalizations. Specifically, the present FOM approach yields stricter efficiency limits applicable to realistic PV absorbers with various imperfections, including finite carrier mobilities and doping densities. ΓPV is a function of eight properties of the absorber that are both measurable by experiment and computable by electronic structure methods. They are: band gap, non-radiative carrier lifetime, carrier mobility, doping density, static dielectric constant, effective mass, and two parameters describing the spectral average and dispersion of the light absorption coefficient. ΓPV has high predictive power (absolute efficiency error less than ±1.1% ) and wide applicability range. The SQ limit and its generalizations are reproduced by ΓPV . Simpler FOMs proposed by others are also included as special cases of ΓPV .