Layer-by-Layer Self-Assembly of Hollow Nitrogen-Doped Carbon Quantum Dots on Cationized Textured Crystalline Silicon Solar Cells for an Efficient Energy Down-Shift

Enhancing the efficiency of the crystalline silicon solar cell (c-Si SC) by coating the energy shifting layer with quantum dots (QDs) is a recent approach to efficiently utilize the high-energy spectrum of light. Carbon QDs are an attractive candidate for such applications; however, a small Stokes shift and nonuniform coating due to high aggregation are the bottlenecks to fully utilize their potential. For this purpose, here, we propose a layer-by-layer self-assembled uniform coating of eco-friendly red-emissive hollow nitrogen-doped carbon QDs (NR-CQDs) as an efficient energy-down-shifting layer. A unique hollow and conjugated structure of NR-CQDs was designed to achieve a large Stokes shift (UV-excited red emission) with a quantum yield (QY) comparable to Cd/Pb QDs. A highly uniform coating of intrinsically negatively charged NR-CQDs on c-Si SCs was achieved by cationizing the c-Si SC by bovine serum albumin (BSA) under mildly acidic conditions. By an opposite-charge-assisted, self-assembled overlayer, the short-circuit current density (Jsc) and power-conversion efficiency were increased by 5.8%, which is attributed to the large Stokes shift (255 nm) and high QY. Blue-emissive undoped carbon QDs were synthesized for comparison with the proposed NR-CQDs to elucidate the significance of the novel proposed structure.