Incorporation of copper–indium back-end layers in the solution-based Cu(In, Ga)Se2 films: enhancement of photovoltaic performance of fabricated solar cells

The morphology and photovoltaic properties of the solution-based Cu(In, Ga)Se 2 films are effectively improved via the incorporation of copper-indium back-end layers in the precursor films. The effects on the concentrations of bimetal-ions solutions to prepare copper-indium back-end layers are investigated in this study. The incorporation of copper-indium back-end layer in the precursor film enhances the internal diffusion between gallium-ions and indium-ions during selenization reaction. Hence, the porous structure in the back-contact region of prepared CIGS films becomes densified, and the bandgap distribution of films shows a gradient profile. The densified morphology and gradient bandgap reduce the carrier recombination and improve the carrier collection of solar cells. In contrast to the pristine precursor film, the precursor film with a copper-indium back-end layer increase the conversion efficiency of prepared solar cells from 8.34% to 11.13%. The enhancement of conversion efficiency is attributed to the improvement of short-circuit current density and fill factor from 25.70 mA cm −2 to 31.79 mA cm −2 and 57.65% to 65.70%, respectively. This study reveals that the photovoltaic properties of solution-based CIGS solar cells can be improved significantly via the incorporation of copper-indium back-end layers into the precursor films.