TADF-LDS · Visually Attractive Photovoltaic Panels without Efficiency Loss

Photovoltaic (PV) technology has proven to be the most promising, economic, and clean solution to the global energy crisis. Over the years, tremendous advancements have been accomplished in the solar PV industry in terms of installations, cost reductions and technological advancements. Crystalline silicon (c-Si) panels belong to the first-generation solar PV and hold ~ 95% share of worldwide PV production. The energy conversion efficiency of silicon solar cells in the lab reached a record value of 26.7% in 2017. An important factor affecting the efficiency of Si solar cells is the poor spectral response of Si below 450 nm. Luminescent Down-Shifting (LDS) is an efficient optical approach used for increasing PV device spectral response by converting high energy photons to lower energy photons. LDS can also be used to modify and enhance the visual appearance of solar panels for building-integrated PV applications. To date various luminescent materials like inorganic phosphors and glasses, colloidal QDs, organic dyes and organolanthanides have been studied as LDS layer in different PV devices. Organolanthanide complexes have proven to be attractive candidates to improve the EQE of solar cells compared to other LDS materials due to their uniquely large spectral shift of emission. Their major drawback to date however, is poor light harvesting in the 350 – 450 nm spectral region while simultaneously maintaining high PL quantum yield. To achieve a step change in performance of lanthanide complex LDS materials, we will implement for the first time ligands that exhibit thermally activated delayed fluorescence (TADF), since these may achieve close to 100% ligand to metal sensitization efficiency, even at near-UV and visible wavelengths. This unique method will extend the absorption range of Ln complexes (from <385 nm to <470 nm) with enhanced absorption coefficient, while achieving improved overall quantum yield of Ln complexes and hence overall improved EQE of PV cells.