Development of CuInSe_2 thin films by SELD method for photovoltaic absorber layer application

摘要

CuInSe_2 (CIS) films were obtained on annealing of 280 nm and 775 nm thick Cu/In/Se stacks deposited on corning glass substrate. The stacked elemental layer deposition (SELD) technique was used for the deposition of the films of Se, In and Cu layers. The as-deposited and annealed samples were found to possess polycrystalline structures. The films provided dominating CIS phase along with secondary phases of Cu_(11)In_9, CuSe and Se. The secondary phases present in the films vary with change in annealing temperatures. Moreover, single CuInSe_2 phase is observed in the 280 nm films at 523 K. The scanning electron microscopic images of the samples show nano-rod type structures of CIS grains. The elemental composition of Cu:In:Se approaches 1:1:2 in 280 nm thick samples. The ratio, however, deviates in the 775 nm thick films. The Raman spectra of these samples give A_l mode at 173 cm~(-1) and confirm the presence of CIS phase. The films exhibit slow increase in the band gap (E_g) values from 1.09 to 1.22 eV for 775 films. However, comparatively higher band gap (E_g) values from 1.25 to 1.90 eV are observed for 280 nm films with high absorption co-efficient (α～ 10~5 cm~(-1)) values. The films present more useful electrical parameters for 280 nm thick samples as compared to 775 nm samples due to dominated CIS phase. Thus, obtained CIS thin films of 280 nm thickness provide viable alternative as an absorber layer in solar cell structure.