Nonradiative Recombination Dominates Voltage Losses in Cu(In,Ga)Se2 Solar Cells Fabricated using Different Methods

Voltage losses reduce the photovoltaic conversion efficiency of thin-film solar cells and are a primary efficiency limitation in Cu(In,Ga)Se-2. Herein, voltage loss analysis of Cu(In,Ga)Se-2 solar cells fabricated at three institutions with variation in process, bandgap, absorber structure, postdeposition treatment (PDT), and efficiency is presented. Nonradiative voltage losses due to Shockley-Read-Hall charge carrier recombination dominate and constitute >75% of the total compared to <25% from radiative voltage losses. The radiative voltage loss results from nonideal absorption and carriers in band tails that stem from local composition-driven potential fluctuations. It is shown that significant bulk lifetime improvements are achieved for all alkali PDT processed absorbers, chiefly associated with reductions in nonradiative recombination. Primary voltage loss contributions (radiative and nonradiative) change little across fabrication processes, but variation in submechanisms (bulk lifetime, net acceptor concentration, and interface recombination) differentiate nonradiative loss pathways in this series of solar cells.