Approaching the Theoretical Efficiency of Kesterite Solar Cells: Analysis of Radiative and Non-Radiative Losses in Cu2ZnSn(S,Se)4

Cu ₂ ZnSn(S,Se) ₄ is among the most promising inorganic photoabsorbers for thin film solar cells. Characteristics such as a high absorption coefficient, solution-processability, and earth-abundant constituents highlight its potential for large-scale photovoltaics. However, the photovoltaic performance of Cu ₂ ZnSn(S,Se) ₄ has so far been hindered by open-circuit voltage losses (ΔV _OC ) in the radiative (ΔV _OC ^Rad ) and non-radiative limit (ΔV _OC ^Nrad ), due to sub-bandgap absorption and deep defect states, respectively. Suppressing these two major loss factors could propel Cu ₂ ZnSn(S,Se) ₄ towards commercial relevance. In the past 2 years, record efficiency approaching 15% has been reported, prompting a renewed interest that the performance-limiting factors have been overcome. In this perspective, we quantify the ΔV _OC for the recently reported high power conversion efficiency devices, compare the relevant photovoltaic metrics to previous records, and offer directions for future research. We find that ΔV _OC ^Rad _{due to bandgap fluctuations and Urbach tails has been suppressed in the recent record devices, with values approaching those for record efficiency Cu(In,Ga)(S,Se) 2 solar cells. However, we also find that the recombination parameter J 0 , which more closely relates to the ΔV OC ^Nrad , ^{only shows modest improvements compared to previous records, and has values that must be improved by about four to six orders of magnitude to compete with those for Cu(In,Ga)(S,Se) 2 solar cells. The impressive performance gains that have been achieved by suppressing ΔV OC Rad must now be built upon to suppress ΔV OC Nrad . Our analysis points out that the next level of breakthrough in power conversion efficiency will be achieved by reducing the non-radiative recombination due to deep defects in the bulk, and at grain boundaries and interfaces.}}