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Understanding what limits the voltage of polycrystalline CdSeTe solar cells

Abstract

The origin of voltage deficits in polycrystalline cadmium selenide telluride (CdSeTe) solar cells is unclear. Here, we present a comprehensive voltage loss analysis performed on state-of-the-art CdSeTe devices—fabricated at Colorado State University and First Solar—using photoluminescence techniques, including external radiative efficiency (ERE) measurements. More specifically, we report the thermodynamic voltage limit Voc,ideal, internal voltage iVoc and external voltage Voc of partially and fully finished cells fabricated with different dopant species, dopant concentrations and back contacts. Arsenic-doped aluminium-oxide-passivated cells made at Colorado State University present remarkably high ERE (>1%)—translating into iVoc above 970 mV—but suffer from poor back-contact selectivity. On the other hand, arsenic-doped devices from First Solar present almost perfect carrier selectivity (Voc = iVoc), leading to Voc above 840 mV, and are limited by recombination in various parts of the device. Thus, development of contact structures that are both passivating and selective in combination with highly luminescent absorbers is key to reducing voltage losses.

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Fig. 1: Impact of dopant species and back-contact structure on sub-band-gap features.
Fig. 2: ERE of CdSeTe devices fabricated with varying dopant species and back contacts.
Fig. 3: Voltage loss analysis of As-doped and Cu-doped CdSeTe samples using baseline Te and passivating back contacts fabricated at Colorado State University.
Fig. 4: Voltage loss analysis of As-doped CdSeTe devices fabricated by First Solar with increasing As incorporation.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and Supplementary Information files. First Solar’s data, beyond what is presented in the manuscript and the Supplementary Information, are proprietary and are not publicly available. Source data are provided with this paper.

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Acknowledgements

The information, data or work presented herein was funded in part by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, under award numbers DE-EE0008552 (A.O., C.L., S.L., A.D., W.W., A.B., D.K., W.S. and Z.C.H.) and DE-EE0008557 (C.L. and W.S.). Funding was provided in part by the National Science Foundation under award no. 1846685 (Z.C.H.). This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the US Department of Energy (DOE) under contract no. DE-AC36-08GO28308 (D.K.). The views expressed herein do not necessarily represent the views of the DOE or the US Government. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for US Government purposes. We thank Y.-H. Zhang and his team at Arizona State University for building and providing access to the ERE measurement tool and J. Sites and his team at Colorado State University for building and providing access to the EQE and C–V measurement tools. We thank R. Pandey, T. Shimpi and J. Sites at Colorado State University, along with G. Yeung and C. Wolden at Colorado School of Mines, for providing some of the samples reported in this study. We thank 5N Plus for providing the CdTe, CdSeTe and CdCl2 source materials. First Solar authors acknowledge support from numerous colleagues and thank D. Martinez and K. Theis for sample preparation and analysis.

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Authors

Contributions

A.O. and Z.C.H. conceived the project. A.O., C.R., A.D., S.G. and D.K. designed the methodology. A.O., C.R., S.L. and D.K. performed the formal analysis. A.O., C.R., S.L., A.D., W.W., A.B., S.G., J.B. and D.K. carried out the investigations. S.G., D.K., W.S. and Z.C.H. provided resources. A.O. wrote the original draft and A.O., C.R., A.D., A.B., S.G., D.K., W.S. and Z.C.H. reviewed and edited the manuscript. A.O. performed the visualization. D.K., W.S., G.X. and Z.C.H. supervised the project. A.O., D.K., W.S. and Z.C.H. acquired funding.

Corresponding authors

Correspondence to Arthur Onno or Zachary C. Holman.

Ethics declarations

Competing interests

S.G., J.B. and G.X. work at First Solar, which is a publicly traded company that manufactures CdTe solar modules. Outside of this, the authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Discussions 1–4, Methods 1–3, Tables 1–5 and Figs. 1–19.

Reporting Summary.

Supplementary Data 1

Statistical source data for Supplementary Figs. 14 and 15 and Supplementary Tables 3–5.

Supplementary Data 2

Source data for Supplementary Fig. 9.

Supplementary Data 3

Statistical source data for Supplementary Fig. 11.

Supplementary Data 4

Time-resolved photoluminescence decays for samples shown in Fig. 2a,b and Supplementary Figs. 7 and 9.

Supplementary Data 5

Capacitance–voltage profiles for samples shown in Fig. 2b and Supplementary Figs. 9 and 19.

Source data

Source Data Fig. 2

Statistical source data for Fig. 2.

Source Data Fig. 3

Statistical source data for Fig. 3.

Source Data Fig. 4

Statistical source data for Fig. 4.

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Onno, A., Reich, C., Li, S. et al. Understanding what limits the voltage of polycrystalline CdSeTe solar cells. Nat Energy 7, 400–408 (2022). https://doi.org/10.1038/s41560-022-00985-z

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