Articulating effect of low copper content on structure and optoelectronic properties of spray deposited Cu2ZnSnS4 thin films – From experiment and first-principles investigations

Abstract Improvement in the efficiency of truly inexpensive spray-pyrolysed Cu2ZnSnS4 (CZTS) thin film solar cells demands both the minimal presence of secondary phases as well as low carrier concentration. The present work deals with a strategy to obtain high quality spray pyrolysed CZTS films with low carrier concentration by controlling Cu-precursor concentration ([Cu2+]). By reducing [Cu2+] from 0.0136 M to 0.0129 M, film’s microstrain changes from compressive (1.76 × 10−3) to tensile (5.89 × 10−3) in nature, allowing the suppression of secondary phase formation. At an optimally low [Cu2+] of 0.0122 M the film shows pure phase, a lower tensile strain and a free carrier concentration of 3 × 1018 cm−3 with p-type conductivity and a high mobility of 3.22 cm2/Vs. Interfacial charge transfer is also promoted in this condition which is verified from electrochemical impedance spectroscopy. Moreover, the consequence of the modulation in the electrical properties through precursor [Cu2+] on the electronic structure and its optical absorption properties are corroborated from first-principles calculation.