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Point defect engineering in thin-film solar cells

Nature Reviews Materials volume 3, pages 194–210 (2018)Cite this article

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Abstract

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.

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Fig. 1: Crystal structure and electronic band structure of Si, CdTe, CuInSe2 and CH3NH3PbI3.
Fig. 2: Formation energy of intrinsic point defects in CdTe under different growth conditions.
Fig. 3: Atomic chemical potentials that stabilize the formation of CZTS and the formation energy of point defects under two growth conditions.

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Acknowledgements

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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  1. Thomas Young Centre and Department of Materials, Imperial College London, London, UK

    Ji Sang Park, Sunghyun Kim, Zijuan Xie & Aron Walsh

  2. Department of Physics, Harbin Institute of Technology, Harbin, China

    Zijuan Xie

  3. Department of Materials Science and Engineering, Yonsei University, Seoul, South Korea

    Aron Walsh

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  1. Ji Sang Park
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All authors researched data for the article and contributed to the discussion of content. J.-S.P., S.K. and A.W. wrote the article, and Z.X. edited and reviewed the article prior to submission.

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Park, J.S., Kim, S., Xie, Z. et al. Point defect engineering in thin-film solar cells. Nat Rev Mater 3, 194–210 (2018). https://doi.org/10.1038/s41578-018-0026-7

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