Formation of interfacial CdTe1−x S x solid solutions in CdTe/CdS heterojunctions

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

“…The internal electric eld due to the gradient in the band gap is a drag eld, which seems to be responsible for the enhanced photosensitivity of the device structure. 285 Thus, a gradual change in the hetero-interface structure decreases the tunneling current and optical losses due to the similar changes in index. [284][285][286][287] The increase of sulfur content increases the band gap of the ternary compound except for the sulfur concentration below 25%, where the band gap decreases due to the bowing effect, leading to a decrease in the low-energy cut off of the device relative to pure CdTe.…”

“…285 Thus, a gradual change in the hetero-interface structure decreases the tunneling current and optical losses due to the similar changes in index. [284][285][286][287] The increase of sulfur content increases the band gap of the ternary compound except for the sulfur concentration below 25%, where the band gap decreases due to the bowing effect, leading to a decrease in the low-energy cut off of the device relative to pure CdTe. 279,288 The bowing effect depressed the band gap of the ternary compound by 0.1 eV lower than the band gap of CdTe with the addition of 30% CdS.…”

“…The composition of a solid solution (x) can be determined from its lattice parameter 'a', which is intermediate between those of CdS (a ¼ 5.832 Å) and CdTe (a ¼ 6.423 Å) using Vegard's law, assuming E g is a linear function of 'a'. 285 The sulfur content 'x' of an CdTe 1Àx S x lm was quantitatively determined from the lattice parameter by assuming Vegard's relationship: x ¼ 1.508(6.481 À a), with 'a' being the lattice parameter of the sample. 269 Optical measurements also supported the formation of ternary alloys that reduced the photoresponse at shorter wavelength and slightly extended response at longer wavelength.…”