Luminescent Solar Concentrators based on Carbon Dots

Abstract

The sustainable use of sunlight for renewable and clean energy production has gained significant attention, leading to the development of solar technologies. However, achieving high solar-to-electrical power conversion efficiency (PCE) at a low cost remains a challenge for solar cells. Luminescent solar concentrators (LSCs) are a promising solution for enhancing solar cell efficiency by capturing and guiding sunlight to small-area solar cells using large-area collectors. To achieve high-efficiency LSCs, it is crucial to synthesize fluorophores with excellent optical properties, such as broad absorption spectrum, high quantum yield (QY), large Stokes shift, and good stability. Carbon quantum dots (CDs) are a type of fluorophores that offer advantages such as a wide absorption spectrum, high quantum yield, non-toxicity, environmental friendliness, low cost, and eco-friendly synthesis methods. However, CDs have a relatively small Stokes shift compared to inorganic quantum dots, which limits their external optical efficiency. To overcome this limitation, doping CDs with metal ions can improve their optical properties and make them suitable for use in LSCs. The study reports on the synthesis of novel Copper (Cu) and Manganese (Mn) doped carbon nanodots (Cu-CDs and Mn-CDs) separately, as the choice of metal ion for doping CDs depends on the desired optical properties of the LSC. The synthesis method utilizes a facile and scalable solvothermal approach to prepare both doped and non-doped CDs, which are then characterized using various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy, spectrofluorometer, and photoluminescence spectroscopy. The results reveal that both Mn-CDs and Cu-CDs exhibit strong photoluminescence with tunable emission wavelengths in the visible range, making them suitable for LSC applications. The introduction of Mn and Cu ions in the CDs creates new energy levels, leading to improved luminescent properties, and the doped CDs exhibit a red-shifted emission compared to pure CDs, suggesting different energy transfer mechanisms in the doped CDs. Moreover, the bandgap was reduced from 2.43 eV (CDs) to 1.65 eV (Cu-doped CDs) and 2.04 eV (Mn-doped CDs) suggesting that the energy level decreases and the thickness of the band becomes thinner. The findings indicate that after metal doping, CDs previously determined stoke shift, which was 0.51 eV, changed to 0.55 and 0.53 eV for Mn-CDs and Cu-CDs, respectively. With metal ion doping, the time decay for CDs increased noticeably from 5.69 ns to 6.69 and 6.47 ns for Cu-CDs and Mn-CDs, respectively. This study also investigates the effect of doping concentration and synthesis parameters on the luminescent properties of the CDs. Furthermore, the LSC performance of the Mn-CDs and Cu-CDs by fabricating LSC prototypes using the doped CDs as luminescent downshifting materials were evaluated. The prototypes are characterized by their optical efficiency and power conversion efficiency. The results demonstrate that Mn-CDs and Cu-CDs effectively enhance the light-harvesting capability of LSCs, leading to improved overall device performance. In conclusion, this study provides valuable insights into the luminescent properties of Mn-doped and Cu-doped carbon dots for LSC applications, contributing to the development of highly efficient and cost-effective LSCs for solar energy harvesting. These findings have potential applications in various fields, including building-integrated photovoltaics, solar windows, and wearable devices. Further optimization of the doping concentration and synthesis parameters could lead to even higher performance of the doped CDs in LSCs, paving the way for their practical implementation in next-generation solar energy harvesting devices.