High Efficiency Aqueous Solution Sprayed CIGSSe Solar Cells: Effects of Zr4+‐Alloyed In2S3 Buffer and K‐Alloyed CIGSSe Absorber

Abstract

AbstractEven though solution‐processed Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells have been developed for long time, their power conversion efficiency (PCE) is still much behind that achieved by vacuum‐based process, and some solvents used in solution‐based processes are not environmental friendly. High‐efficiency CIGSSe solar cells made by using water‐based spray deposition in an air environment are reported. Water is the most eco‐friendly and cheapest solvent compared to the other solvents used in solution‐based fabrication. In2S3‐based buffer (eco‐friendly Cd‐free buffer) and CdS buffer are tested as a buffer layer. For higher PCE with In2S3‐based buffer, a Zr4+‐alloyed In2S3 is used and Zr4+ alloying effects are investigated. It is found that Zr4+ alloying increases the electron concentration in the buffer and passivates defect states in the CIGSSe absorber, which enhance PCE significantly. On the other hand, it is found that K‐alloying into the CIGSSe absorber passivates defects in the CIGSSe absorber, which further increases PCE. Owing to the observed beneficial effects, highest PCE of 16.08% and 17.74% is achieved with Zr4+‐In2S3 buffer and CdS buffer, respectively. In addition, since fabricated solar cells are made with bandgap below 1.15 eV, they can be utilized as a bottom cell for high efficiency tandem cell.