Enhanced charge transport and photovoltaic performance induced by incorporating rare-earth phosphor into organic-inorganic hybrid solar cells

In this work, dysprosium ion decorated yttrium oxide (Dy³⁺:Y₂O₃) nanocrystal phosphors were incorporated into TiO₂ acceptor thin film in a bid to enhance the light harvest, charge separation and transfer in the hybrid solar cells. The results show that the energy level offset between the donor (P3HT) and the acceptor (Dy³⁺:Y₂O₃-TiO₂) has been narrowed down, thus leading to the enhanced electron and hole transports, and also photovoltaic performances as compared to pure TiO₂ without incorporating Dy³⁺:Y₂O₃. By applying femtosecond transient optical spectroscopy, after the incorporation of dopant Dy³⁺:Y₂O₃ into TiO₂ at 6 wt%, both the hot electron and hole transfer lifetimes have been shortened, that is, from 30.2 ps and 6.94 ns to 25.1 ps and 1.26 ns, respectively, and an enhanced efficiency approaching 3% was achieved as compared to 2.0% without doping, indicating that the energetic charges are captured more efficiently benefitting a higher power conversion efficiency. Moreover, these results reveal that both the conduction band (CB) and valence band (VB) edges of the acceptor were elevated by 0.57 and 0.32 eV, respectively, after incorporating 6 wt% Dy³⁺:Y₂O₃. This work demonstrates that distinct energy level alignment engineered by Dy³⁺:Y₂O₃ phosphor has an important role in pursuing efficient future solar cells and underscores the promising potential of rare-earth phosphor in solar applications.