Control of defect processes in photovoltaic materials is essential for realizing high-efficiency solar cells and related optoelectronic devices. Native defects and extrinsic dopants tune the Fermi level and enable semiconducting p-n junctions; however, fundamental limits to doping exist in many compounds. Optical transitions from defect states can enhance photocurrent generation through sub-bandgap absorption; however, these defect states are also often responsible for carrier trapping and non-radiative recombination events that limit the voltage in operating solar cells. Many classes of materials, including metal oxides, chalcogenides and halides, are being examined for next-generation solar energy applications, and each technology faces distinct challenges that could benefit from point defect engineering. Here, we review the evolution in the understanding of point defect behaviour from Si-based photovoltaics to thin-film CdTe and Cu(In,Ga)Se2 technologies, through to the latest generation of halide perovskite (CH3NH3PbI3) and kesterite (Cu2ZnSnS4) devices. We focus on the chemical bonding that underpins the defect chemistry and the atomistic processes associated with the photophysics of charge-carrier generation, trapping and recombination in solar cells. Finally, we outline general principles to enable defect control in complex semiconducting materials.
Bibliographical noteFunding Information:
The authors thank S.-H. Wei, K.J. Chang, A. Zunger, A.A. Sokol, C.R.A. Catlow, and C.G. van de Walle for illuminating discussions regarding defects in semiconductors. This project has received funding from the European Horizon 2020 Framework Programme for research, technological development and demonstration (Grant No. 720907); see STARCELL for further information. A.W. is supported by a Royal Society University Research Fellowship and the Leverhulme Trust, and J.P. is supported by a Royal Society Shooter Fellowship.
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All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Energy (miscellaneous)
- Surfaces, Coatings and Films
- Materials Chemistry