Manifestation of the Enhanced Photovoltaic Performance in Eco-Friendly AgBiS2 Solar Cells Using Titanium Oxynitride as the Electron Transport Layer

In this study, titanium oxynitride with empirical composition of TiON is developed using a sol–gel and ammonia-gas-assisted thermal nitridation process. The obtained TiON phase is employed as the photoanodic electron transport layer (ETL) in a silver bismuth sulfide (AgBiS2) quantum-dot-sensitized solar cell (QDSSC) device and compared to a QDSSC consisting of commercial TiO2 as the ETL. The obtained X-ray photoelectron spectroscopy spectra and Mott–Schottky plots of the samples suggested that the valence and conduction bands of TiON are significantly shifted (EVB = 2.9 eV and ECB = −0.3 eV) with respect to that of TiO2 (EVB = 1.88 eV and ECB = −0.51 eV), which eventually decreased its band gap energy to 2.46 eV compared to TiO2 (3.2 eV). A decrease in the charge transfer resistance (Rct = 38.2 Ω) and improvement in carrier lifetime (τ = 5.3 ms) are observed in the developed TiON device. The work also endorses the use of eco-friendly green quantum dots of AgBiS2 as photoabsorbers in solar cells. Although the photovoltaic performance is not found to be greater, the demonstration of the enhanced performance of the TiON-based device with ∼50% enhancements, owing to its improved open circuit voltage and current density by 20 and 35%, is achieved in this work. Titanium oxynitride can, hence, be considered a suitable alternative to existing commercial TiO2 in all applications that involve solar energy conversion.