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Cu2ZnSnS4 solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment


Sulfide kesterite Cu2ZnSnS4 provides an attractive low-cost, environmentally benign and stable photovoltaic material, yet the record power conversion efficiency for such solar cells has been stagnant at around 9% for years. Severe non-radiative recombination within the heterojunction region is a major cause limiting voltage output and overall performance. Here we report a certified 11% efficiency Cu2ZnSnS4 solar cell with a high 730 mV open-circuit voltage using heat treatment to reduce heterojunction recombination. This heat treatment facilitates elemental inter-diffusion, directly inducing Cd atoms to occupy Zn or Cu lattice sites, and promotes Na accumulation accompanied by local Cu deficiency within the heterojunction region. Consequently, new phases are formed near the hetero-interface and more favourable conduction band alignment is obtained, contributing to reduced non-radiative recombination. Using this approach, we also demonstrate a certified centimetre-scale (1.11 cm2) 10% efficiency Cu2ZnSnS4 photovoltaic device; the first kesterite cell (including selenium-containing) of standard centimetre-size to exceed 10%.

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This contribution has been financially supported by the Australian Government through the Australian Renewable Energy Agency (ARENA) (grant no. 1-USO028 and 1-SRI001) and the Australian Research Council (ARC) and Baosteel (grant no. LP150100911). The authors thank C. Kong and K. Levick for technical assistance and use of facilities at the Electron Microscope Unit at University of New South Wales. The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy and Microanalysis Research Facility at the Australian Centre for Microscopy and Microanalysis at the University of Sydney. The authors appreciate the use of facilities and the assistance of D. Mitchell and G. Casillas Garcia at the University of Wollongong Electron Microscopy Centre. We thank R. Liu at the Western Sydney University SIMS Facility. C.Y. would like to acknowledge the insightful discussions with Z. Su, H. Sugimoto, H. Hiroi and A. Crovetto.

Author information

M.A.G. and X.H. supervised the whole project. C.Y., F.L. and X.H conceived the idea and designed the experiments. C.Y. and Y.Z. fabricated the solar cell devices. J.H. prepared TEM specimens and performed HAADF characterizations. K.S. assisted TRPL characterizations. S.J. conducted temperature-dependent measurements. L.Y. and K.E. prepared APT samples and conducted APT measurements, respectively. C.Y., J.H., K.S., A.P., S.J., K.E., J.M.C., N.J.E.-D., S.C., Z.H. and H.S. analysed the data. Z.H., F.L. and M.H. helped with characterizations, J.A.S., F.L., H.S. and M.H. assisted the experiments. C.Y., J.H., X.H. and M.A.G. wrote the paper. All authors commented on the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to Fangyang Liu or Xiaojing Hao.

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Further reading

Fig. 1: Photovoltaic device properties for the 11.0% efficient solar cell.
Fig. 2: Recombination origin analyses.
Fig. 3: Elemental inter-diffusion and high-resolution imaging.
Fig. 4: Accumulation of Na.
Fig. 5: Band alignment at the p–n junction.