Abstract
Earth abundant copper–zinc–tin–chalcogenide is an attractive class of materials for the fabrication of high efficiency, low cost, and sustainable thin-film solar cells. A CZTSSe solar cell was modeled and the effects of absorber layer band-gap grading were investigated. Regarding the tunable bandgap of kesterite absorber layers which is between 0.95 eV for CZTSe and 1.5 eV for CZTS, several grading models were simulated in SCAPS. First, using a set of comprehensive absorption data for CZTS and CZTSe, the basic bandgap was selected to be 1.15 eV due to experimental aspects, and then, five grading models namely back/front linear, back/front exponential, and inside graded were explored. The investigation of simulation results showed that the recombination rate improvement in back and front regions along with current density enhancement is achievable by these graded band-gap profiles. Finally, the modified inside graded model was reached to a power conversion efficiency of 15.6% which leaded to a considerable output performance.
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