High-Efficiency Self-Powered Photodetector for UV-Visible-NIR Spectrum Using Solution-Processed TiO2/Cu2ZnSnS4 Heterojunction in Superstrate Configuration

This study introduces a sustainable and efficient approach for self-powered photodetection using a solution-processed TiO₂/CZTS heterojunction to detect the broad electromagnetic spectrum. CZTS thin films with a pure kesterite phase are synthesized via a cost-effective sol-gel spin coating technique, eliminating the need for high-temperature post-deposition sulfurization. The formation of the kesterite phase in CZTS films is confirmed through microstructural studies, Raman spectroscopy, and optical analyses. A high-quality heterojunction is fabricated by depositing the CZTS layer on chemically synthesized TiO₂ thin film on FTO-coated glass substrates, and its photoresponse characteristics are studied under 365 nm, 405 nm, 532 nm, 650 nm, and 980 nm light in a superstrate configuration. The heterojunction exhibits optimal photoresponsivity (~1.28 mA/W), detectivity (~4.77 ×10¹⁰ Jones), and rise/decay times (~54 ms/27 ms) at zero external bias. It also demonstrates efficient performance under 1 sun AM1.5 G solar spectrum. The photodetection mechanism through carrier dynamics under illumination for the heterostructure is further investigated using impedance spectroscopy, incident light-dependent capacitance-voltage characteristics, and photo-capacitance measurements. This approach provides a cost-effective and scalable solution for self-powered photodetection, offering significant potential for integration into various optoelectronic devices for renewable energy harvesting and sensing applications.