Rapid growth of thin Cu(In,Ga)Se 2 layers for solar cells

Abstract

In this study, we have decreased the deposition time from 60 min down to 3.75 min for three sets of Cu(In,Ga)Se 2 (CIGS) layers: baseline CIGS (≈2 μm thick and homogeneous composition), Ga-graded CIGS (≈2 μm thick) and Ga-graded thin CIGS (≈1 μm thick). The CIGS layers were fabricated with co-evaporation and analysed with a scanning electron microscope and X-ray diffraction. The complete devices were analysed with I– V and quantum efficiency. By reducing the deposition time from 60 to 3.75 min, the efficiency was reduced from 14.7% down to 12.3% (for the baseline CIGS). This reduction is explained by increased recombination, which correlates with decreased grain size for CIGS layers with shorter deposition times. In order to decrease the deposition time, with a maintained high efficiency, a 1.8–2 μm thick CIGS layer with a Ga-gradient is shown to be the best alternative down to 7.5 min deposition time, at which a CIGS layer, resulting in a 14.6% efficient solar cell, was fabricated. At 3.75-min deposition time the efficiency was improved when the CIGS thickness was reduced from 2 μm down to 1 μm.