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

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 x 10(-3)) to tensile (5.89 x 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 x 10(18) cm(-3) with p-type conductivity and a high mobility of 3.22 cm(2)/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.

Automated summary

By controlling the copper precursor concentration, high quality spray pyrolysed CZTS films with low carrier concentration can be obtained, allowing for the suppression of secondary phase formation and achieving characteristics such as pure phase, low tensile strain, and high mobility at an optimally low copper precursor concentration of 0.0122 M. Interfacial charge transfer is promoted in this condition, and the modulation of electrical properties through precursor copper concentration on the electronic structure and optical absorption properties is confirmed through first principles calculation.