Point defect engineering in thin-film solar cells

Control of defect processes in photovoltaic materials is essential for realising high - efficiency solar cells and related optoelectronic devices. The concentrations of n ative defects and e xtrinsic dopants tune the Fermi level and enable semiconducting p - n junctions; however, fundamental limits to doping exist in many compounds. Optical transitions involving defect states can enhance photocurrent generation through sub - bandgap absorption; ho wever, such states are often responsible for carrier trapping and non - radiative recombination events that limit open - circuit voltage. Many classes of materials – including metal oxides, chalcogenides , and halides – are being examined for next - generation so lar energy applications, and each technology faces distinct challenges that could benefit from point defect engineering . We review the evolution in point defect behaviour from Si - based photovoltaics to thin - film CdTe and Cu(In,Ga)Se 2 technologies, through to the latest generation halide perovskite (CH 3 NH 3 PbI 3 ) and kesterite (Cu 2 ZnSnS 4 ) devices. We focus on the chemical bonding that underpins the defect chemistry, and the atomistic processes associated with the photophysics of charge carrier generation, trap ping , and recombination in solar cells. Finally, we outline general principles to enable defect control in complex semico nducting materials