Enhancing CZTSSe solar cell efficiency to 11.07% with NaClO-induced Mo texturing for improved light management and carrier collection

Abstract

This study systematically investigates the optimization mechanism of NaClO solution treatment on Mo substrates for enhancing the optoelectronic performance of CZTSSe thin film solar cells. Experimental results demonstrate that a 10 s NaClO soaking forms a “spike-like” texture on the Mo surface, increasing the average surface roughness difference from 34.52 to 77.75 nm. This significantly enhances light scattering, particularly for photons reaching the back Mo electrode, thereby extending the optical path and promoting photon reabsorption. Additionally, the roughened Mo surface improves the wettability of the precursor solution (contact angle decreases from 19.3° to 12.7°), facilitating the formation of larger CZTSSe grains. Electrical characterization reveals that the NaClO-treated Mo substrate significantly reduces the density of negative charge traps at CZTSSe grain boundaries (contact potential difference increases from −1.1 V to −263 mV), suppressing hole recombination and optimizing carrier collection efficiency. The spike-like structure of the Mo surface also shortens the transport path of hole carriers generated by short-wavelength light, further enhancing collection efficiency. Ultimately, the PCE of CZTSSe devices based on the Mo-10 substrate increases from 9.34% to 11.07%, attributed to the reduction in Rs and J0. This study highlights the critical role of a back electrode interface microstructure design in synergistically optimizing light absorption and carrier transport.