Emerging trends in lanthanide-based upconversion and downconversion material for PSCs & DSSCs

This review thoroughly analyzes the progress and challenges in the emerging fields of rare-earth-based upconversion (UC) and downconversion (DC) materials for dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). Despite being outperformed by silicon solar cells in terms of efficiency, DSSCs and PSCs have garnered significant attention owing to their ease of fabrication using low-cost materials, making them promising alternatives for commercial photovoltaic devices. However, their power conversion efficiency (PCE) is limited by significant absorption in the visible region of the solar spectrum, leading to transmission losses of sub-bandgap photons. Rare-earth-doped luminescent materials provide a favorable solution by converting these low-energy photons into high-energy photon, thereby enhancing the light absorption and scattering effects of solar cells. This review delves into the underlying mechanisms of trivalent lanthanide ions, which exhibit exceptional luminescence, photostability, and sharply defined emission lines. The review also discusses the impact of microstructures on the properties and performance of these solar cells, emphasizing the importance of energy band alignment, defect passivation, and charge carrier transport facilitated by rare-earth doping. Additionally, this review covers fabrication techniques and discusses the broader implications of UC and DC materials in advancing future photovoltaic technologies. Further, this review offers a comprehensive perspective on the potential applications and future trends in integrating rare-earth-based materials into solar cells, aiming to maximize their efficiency and commercial viability.