Identifying and comparing efficiency-loss mechanisms in earth-abundant thin-film solar cells

Given scaling limitations on conventional thin-film solar cell semiconductors (e.g., CdTe, CuIn_1-xGa_xSe₂), there is increased interest in developing earth-abundant absorbers such as Cu₂O, SnS, and CZTS (CuZn_1-xSn_xS₂). These devices have historically suffered from poor efficiencies, slow to improve over the last few decades. Accelerating this development will be critical in enabling terawatt-scale photovoltaics competitive with grid electricity prices. The present work identifies the predominant efficiency-loss mechanisms in Cu₂O, as a test case for other earth-abundant absorbers. In particular, the importance of bulk lifetime, surface recombination, and interface band offsets are highlighted. Lessons may be extended to other earth-abundant absorbers in order to compare loss mechanisms and to identify which bulk, interface, and device loss mechanisms dominate for a given absorber material. Approaches including optical engineering, lower work function front contacts, atomic layer deposition of the buffer layer, and improving bulk material properties can lead to significantly higher efficiencies.