Kesterite Cu 2 ZnSnSe 4 (CZTSe), Cu 2 ZnSn(S,Se) 4 (CZTSSe), and Cu 2 ZnSnS 4 (CZTS) solar cells show considerably lower open-circuit voltages than their theoretical values. The large opencircuit voltage deficiency (V oc def ) hinders the improvement of the power conversion efficiency (PCE) and the development of the pathway to mass production of kesterite solar cells. The main reason behind the V ocdef is considered to be the low formation energy of Cu/Zn disorders and their highly distributed defect complexes. To diminish the Cu/Zn disorder, we substituted Ag with a relatively large atomic radius into the host CZTSSe as (Ag x Cu 1−x ) 2 ZnSn(S,Se) 4 (ACZTSSe) and investigated its beneficial effect in a systematic way. The ACZTSSe absorbers were all fabricated using aqueous spray pyrolysis in ambient air. The device performance was found to increase up to the optimum Ag substitution and decrease after the optimum Ag substitution. Admittance spectroscopy revealed that the optimal substitution of Ag reduced the Cu-/Zn-related defects, that is, charge recombination centers, which further mitigates the band tailing issue and enhances the PCE of the solar cell, and higher Ag substitution induced the generation of deeper defects, which decreases the PCE back. At the optimum Ag content of Ag/(Ag + Cu) = ∼9%, the ACZTSSe solar cell with the highest PCE of 11.83% was obtained, where both the interface recombination and bulk recombination were found to be minimized.

(021) and (201)plane with deposition time 20 hours and 22 hours respectively, whereas the major peak at (111)

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This research is focused on a new type of three junction high efficiency solar cell incorporating the promising Si-Ge material as the bottom layer. As a proof of concept, the proposed solar cell has been configured with high quality material of bandgaps 1.9 eV GaInP 2 and 1.42 eV GaAs as top and middle subcells and 0.838 eV bandgap Si 0.38 Ge 0.62 new semiconductor material as bottom subcell. The chosen materials for this configuration are lattice matched (5.66 Å) and this matching is beneficial for optical transparency and current conductivity. The short circuit current density (J sc ), reverse saturation current density (J 0 ), open circuit voltage (V oc ), voltage (V m ) and current density (J m ) at maximum power point, fill factor (FF) and the photoconversion efficiency (η) for the proposed multijunction solar cell (MJSC) have been determined by using the standard solar cell equations of modified spectral p-n junction model and MATLAB in-house code. The ASTM G173-03 reference spectra have been utilized for the quantitative analysis at airmass AM1.5G global irradiance condition. The conversion efficiency of the GaInP 2 /GaAs/Si 0.38 Ge 0.62 solar cell has been simulated as 47.1% at AM1.5G under normal sun (1 sun) concentration and 56.4% under 1000 suns concentration.