Efficiency enhancement of CZTS solar cells using structural engineering

Abstract

We numerically performs structural engineering for lowering interfacial recombination, and enhancing efficiency of CZTS solar cells. Structural modification of controlling carrier density profile at CZTS/CdS interfaces, CZTS absorber surface region carrier density, CZTS surface region bandgap modification, Fermi level pining and tunneling at the CZTS/CdS junction are studied for their impact device performance. We observed that the lowering hole concentration and widening bandgap of CZTS in vicinity of CZTS/CdS junction, lower interface recombination and improve performance. Fermi level pinning near to conduction band edge at CZTS/CdS interface showed lower recombination as compared to the case where Fermi level is pinned at midgap at CZTS/CdS interface. The donor defects from buffer layer pins the Fermi level near conduction band and acceptor defect from absorber CZTS layer pins Fermi level near mid gap at CZTS/CdS interface. Intra band tunneling through high conduction band offset barrier maintain performance for up to 0.5 eV spike barrier. High hole density profile at CZTS/metal lower back contact interfacial recombination. These structural engineering numerical performed here, present bright aspect for improving efficiency of CZTS solar cells. • Device engineering is performed for controlling interfacial recombination in CZTS solar cells. • Absorber surface layer parameters such as carrier density profile and bangap influence interfacial recombination. • Fermi level pinning near conduction band edge is advantageous than Fermi level pinned at midgap at CZTS/CdS interface. • High majority carrier concentration near back contact in CZTS minimize the effect of high Schottky barrier and high SRV.