Sodium and sulfur synergistic incorporation for performance improvement of solution-processed submicron CuIn(S,Se)2 solar cells

Sodium incorporation improves the charge carrier concentration and open-circuit voltage of copper indium disulfoselenide (CISSe) solar cells, improving photovoltaic (PV) performance. Sulfur passivates surface defects, reducing surface recombination and improving PV performance. In this work, we research selenization and simultaneous selenization and sulfurization (Se&S) treatment for solution-processed submicron copper indium sulfide (Cu-In-S) precursor thin films that have been subject to NaCl solution treatment. Na incorporation significantly suppresses both non-radiative and radiative recombination, attributed to reduced recombination coefficients in the space charge region and at the absorber's front interface. Se&S-treated CISSe solar cells (without Na) exhibit higher V oc but lower J sc , FF , and efficiency compared to selenized-only CISSe solar cells. Furthermore, CISSe solar cells fabricated with Na and Se&S synergistic treatment exhibit higher V oc , FF , and efficiency than other recipes, achieving a maximum value of 11.2%, with V oc of 588.9 mV, J sc of 28.8 mA/cm 2 , and FF of 65.9%. Furthermore, a post‑sulfurization process is investigated for the passivation of surface and grain boundaries of the Na-treated CISSe absorber, which however degrades the performances of Na-treated CuInSe 2 . Our research demonstrates that Na and Se&S synergistic treatment for precursor films is a promising strategy for fabricating high-performance solution-processed CISSe solar cells. Na and S incorporation synergistically enhance solution-processed CISSe solar cell performance. This treatment improves absorber crystallinity and passivates surfaces and grain boundaries, reducing both non-radiative and radiative recombination. • Na- and Se&S-treated sub-micron CISSe solar cells achieve 11.2% efficiency. • The synergistic Na and Se&S treatment reduces the recombination coefficients. • Na incorporation suppresses radiative and non-radiative recombination losses. • Post-sulfurization degrades the performance of Na-treated CISSe solar cell.