Morphological engineering of novel nanocrystalline Cu2Sn(S,Se)3 thin film through annealing temperature variation: Assessment of photoelectrochemical cell performance

Abstract

Robust nanocrystalline Cu2Sn(S,Se)3 (CTSSe) thin films have been synthesized for the first time by arrested precipitation technique (APT) through arrest and release of ions from complexed solution and used as potential photocathode for photoelectrochemical cell application. The assessment of annealing temperature variation on the optostructural and optoelectronic performance of CTSSe thin films was studied. It was noticed that the annealing temperature, effectively modifies the absorption and crystalline properties of CTSSe thin films. Optical absorption interpretations elucidated the direct allowed nature of transitions with alteration of band gap energy from 1.68-1.50 eV as the annealing temperature increases. Structural studies from the XRD demonstrates the shifting of diffraction peak to the lower 2θ values with the average crystallite size in the range 19 to 28 nm. A comparative study of XRD and Raman spectra revealed the formation of cubic CTSSe crystal structures. Surface morphological alterations from a small bunch of nanograins to nanorocks to nanocubes were manifested with effective variation in annealing temperature. The compositional studies demonstrates the presence of Cu1+, Sn4+, S2− and Se2− oxidation states in Cu2Sn(S,Se)3 thin film synthesized by APT. Single phase cubic crystal formation from HRTEM and SAED results, verify good crystallinity of synthesized CTSSe thin film. Furthermore, the J-V curves shows the highest photoelectrochemical cell efficiency of 0.42 % for bare CTSSe photocathode with two electrode cell configuration of glass/FTO/Cu2Sn(S,Se)3/(I−/I3−)/graphite. A reduced charge transfer resistance (Rct) from the EIS plots supports for the improved PEC efficiency.