Vacuum evaporated FTO/(Cu, Ag)2ZnSnSe4 thin films and its electrochemical analysis

Abstract

Cu2ZnSnSe4 (CZTSe) and Ag2ZnSnSe4 (AZTSe) thin films were deposited on FTO substrates by the thermal evaporation method and the films were annealed at 300 °C for 2 h. The XRD analysis confirms the formation of tetragonal structure for both CZTSe and AZTSe thin films. The introduction of Ag instead of Cu is confirmed by the major crystalline peak (112) shift towards lower angle 2θ = 26.1° (for AZTSe). In the Raman spectra, the noticeable vibrations appeared at 186 cm−1 and 183 cm−1 confirm the formation of CZTSe and AZTSe thin films. Raman technique also found the presence of SnSe as a secondary phase. By comparing the optical spectra, the AZTSe film has higher absorption in the visible region than the CZTSe thin films which is attributed to the surface plasmon resonance of Ag. AFM images show a pyramidal structure for both CZTSe and AZTSe films. The Mott-Schottky plot shows p-type conductivity for FTO/CZTSe while there is n-type conductivity for a FTO/AZTSe thin film. The variation in the conductivity is due to replacing Cu with Ag. Photoelectrochemical cell (PEC) performance was employed in the presence of a polysulfide electrode by a standard three-electrode system. By comparing the value of Voc, the AZTSe film shows higher Voc than CZTSe films which is important for photovoltaic applications. The Photoconversion efficiency (PCE) is measured to be 0.31% for FTO/AZTSe thin films, while it is low about 0.29% for FTO/CZTSe. The impedance plot shows the semicircular nature for both the FTO/CZTSe and FTO/AZTSe films.