What question did this study set out to answer?

To investigate how selenization temperature impacts the performance of Ge-doped CZTSSe solar cells.

March 29, 2026Materials0 citationsOpen Access

Tuning the Performance of Ge-Doped CZTSSe Solar Cells via Selenization

XLXiaogong Lv SZShumin Zhang YYYanchun Yang

Key Points

To investigate how selenization temperature impacts the performance of Ge-doped CZTSSe solar cells.
Synthesize Ge-doped CZTS precursor films using a green solution approach.
Vary selenization temperatures between 530–570 °C.
Characterize films using XRD, SEM, XPS, EDS, and AFM to assess microstructure and properties.
CZTGSSe films showed the best crystallinity at 550 °C with improved grain growth.
Achieved lowest carrier transport resistance (8.6 Ω∙cm2) and enhanced recombination resistance (5.9 kΩ∙cm2).
Resulting solar cells demonstrated 8.69% power conversion efficiency with VOC of 0.42 V and JSC of 37.71 mA·cm–2.

Abstract

Cu2ZnSn(S,Se)4 (CZTSSe) is a candidate thin-film photovoltaic material; however, its performance is restricted by innate defect-induced nonradiative recombination. Low-concentration Ge doping has been identified as an efficient way to mitigate these defects, but the selenization temperature remains an important process parameter that governs the structure and optoelectronic characteristics of CZTSSe absorbers. In the present work, low-concentration Ge-doped Cu2ZnSn0.95Ge0.05S4 (CZTGS) precursor films were synthesized through a green, n-butylammonium butyrate-based solution approach. The effects of the selenization temperature (530–570 °C) on the microstructure, composition, and photovoltaic performance of Cu2ZnSn0.95Ge0.05(S,Se)4 (CZTGSSe) films and devices were comprehensively investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometer (EDS), atomic force microscopy (AFM) were performed to comprehensively characterize the synthesized samples, and the results suggested that the selenization temperature dramatically altered the film grain growth, crystallinity, elemental retention and surface roughness. Specifically, the film that underwent selenization at 550 °C presented the best crystallinity, which was accompanied by large-scale even grains, efficient Ge4+ addition to the kesterite lattice and the lowest surface roughness. These better properties in terms of structure and composition resulted in the lowest carrier transport resistance (Rs = 8.6 Ω∙cm2), improved recombination resistance (Rj = 5.9 kΩ∙cm2), inhibited nonradiative recombination, and prolonged carrier lifetime (τEIS = 35.8 μs). Therefore, the resulting CZTGSSe thin-film solar cell had an 8.69% better power conversion efficiency (PCE), while its open-circuit voltage (VOC) was 0.42 V, the fill factor (FF) was 55.51%, and the short-circuit current density (JSC) was 37.71 mA·cm–2. Our results elucidate the mechanism by which the selenization temperature regulates low-concentration Ge-doped kesterite devices and provide more insights into the optimization of processes for cost-effective, high-performance, and green thin-film solar cells.

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