UV-Curable Polymer-QD Flexible Films as the Downconversion Layer for Improved Performance of Cu(In,Ga)Se₂Solar Cells

The downconversion process effectively traps high-energy photons of ultraviolet light and converts them into low-energy photons for utilization in solar cells. In this work, transparent, highly emissive, ultraviolet (UV)-curable nitrogen-functionalized graphene quantum dot-dispersed Norland Optical Adhesive (NOA) nanocomposite (herein denoted as poly-QD film) flexible films were applied as luminescent downconversion (LDC) layers to boost the efficiency of copper indium gallium selenide solar cells. The N-graphene quantum dots (GQDs) were embedded into clear, colorless UV-curable NOA polymer matrices via the "click"reaction of thiol-ene components under UV light at room temperature. The best poly-QD film showed a high emission peak of >500 nm and improved external quantum efficiency in the high-energy solar spectrum, resulting in the highest efficiency of ∼9.70% (compared to 8.77% for bare cells), which triggered an ∼10.60% relative performance increment compared to bare copper indium gallium selenide (CIGS) solar cells. Hence, the overall CIGS solar cell performance enhancement caused mainly by Jsc improvement of ∼9.06% (relative enhancement) due to efficient trapping of short-wavelength photons. As-prepared poly-QD films were applied as LDC layers, which significantly boost quantum efficiency in short-wavelength spectra.