Highly Efficient Luminescent Solar Concentrators Based on Capped Carbon Quantum Dots with Unity Quantum Yield

Luminescent solar concentrators (LSCs) can convert sunlight to clean energy by serving as large-area collectors of sunlight. Benefiting from their large-area, semi-transparency, and lightweight characteristics, LSCs have gained a great of attention. However, their optical efficiency is limited by the low quantum yield (QY) and small Stokes shift of conventional photoluminescent materials. Carbon quantum dots (C-dots) are promising alternatives, yet achieving both high QY and large Stokes shift has proven challenging. Here, a simple, controllable vacuum heating method is introduced to synthesize highly efficient C-dots using a citric acid-urea-cyanuric acid-CaCl₂ system. The cyanuric acid-capped C-dots exhibit outstanding properties, including a QY of 94.3% in solution and 100% in a polymer matrix, a large Stokes shift of 0.64 eV, and exceptional photostability, making them ideal for LSC applications. Ultrafast transient absorption spectroscopy provides insights into their exciton dynamics. An LSC (25 cm²) based on these C-dots achieves an optical efficiency of 13.82% ± 0.30%, while its attached photovoltaic cell attains a power conversion efficiency of 4.82% ± 0.10% under natural sunlight (80 mW cm⁻²), marking the highest performance reported for C-dot-based LSCs. These results highlight the potential of cyanuric acid-capped C-dots for advanced solid-state lighting and energy conversion technologies.