High‐Efficiency Luminescent Solar Concentrators Based on Carbon Dots with Simultaneously Ultrabright Solid‐State and Liquid‐State Luminescence

Abstract Carbon dots (CDs) are ideal fluorophores for optoelectronic devices. However, it is still a great challenge to obtain CDs with high solid‐state photoluminescence quantum yields (PLQYs). In this work, it is first reported that the barium‐doped CDs (Ba‐CDs), which can be simply synthesized on a large scale via a direct one‐step heating approach using an open vessel. The as‐synthesized Ba‐CDs exhibit ultrabright luminescence both in liquid and solid states. The as‐synthesized Ba‐CDs with a scale of 8.6 g per batch show a Stokes shift of ≈0.68 eV and high PLQYs of 80.8% and 66.8% in liquid and solid state, respectively. Interestingly, an efficient fluorescence enhancement phenomenon occurs when Ba‐CDs are mixed with polyvinylpyrrolidone (PVP), which reveals the critical issue of compatibility between CDs and polymer matrix can be well resolved. As a proof‐of‐concept, the Ba‐CDs are employed as fluorophores for high‐efficiency luminescent solar concentrator (LSC) fabrication. The Ba‐CDs@PVP‐based LSC has a PLQY of 88.78%, showing a breakthrough optical conversion efficiency of 7.16% and power conversion efficiency of 6.87% under natural light irradiation (40 mW cm⁻²). The results demonstrate the potential application of the ultrabright Ba‐CDs in efficient photovoltaic devices.