Exciton Generation/Dissociation/Charge-Transfer Enhancement in Inorganic/Organic Hybrid Solar Cells by Robust Single Nanocrystalline LnP_<i>x</i>O_<i>y</i> (Ln = Eu, Y) Doping

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron–hole transfer. Inorganic/organic hybrid solar cell, although still in its infancy, has attracted great interest thus far. One of the promising ways to enhance exciton dissociation or electron–hole transport is the doping of lanthanide phosphate ions. However, the underlying photophysical mechanism remains poorly understood. Herein, by applying femtosecond transient absorption spectroscopy, we successfully distinguished hot electron, less energetic electron, hole transport from electron–hole recombination. Concrete evidence has been provided that lanthanide phosphate doping improves the efficiency of both hot electron and “less energetic” electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 12.7 ps, that is, more than 60% faster than pure TiO₂ acceptor. Such improvement was ascribed to the facts that the conduction band (CB) edge energy level of TiO₂ has been elevated by 0.2 eV, while the valence band level almost remains unchanged, thus not only narrowing the energy offset between CB levels of TiO₂ and P3HT, but also meanwhile enlarging the band gap of TiO₂ itself that permits one to inhibit electron–hole recombination within TiO₂. Consequently, lanthanide phosphate doped TiO₂/P3HT bulk-heterojunction solar cell has been demonstrated to be a promising hybrid solar cell, and a notable power conversion efficiency of 2.91% is therefore attained. This work indicates that lanthanide compound ions can efficiently facilitate exciton generation, dissociation, and charge transport, thus enhancing photovoltaic performance

Top-down Strategy toward Versatile Graphene Quantum Dots for Organic/Inorganic Hybrid Solar Cells

Metal oxide nanocrystals have been pursued for various applications in photovoltaics as a buffer layer. However, it remains a challenging task to adjust their energy levels to achieve a better match of the donor–acceptor system. Herein, we report the fabrication of graphene quantum dots (GQDs) with bright blue photoluminescence by a top-down strategy based on laser fragmentation with posthydrothermal treatment. The GQDs demonstrate appropriate energy level positions and are used as an intermediate buffer layer between TiO₂ and P3HT to form a cascade energy level architecture. The introduction of the GQDs into a bulk heterojunction hybrid solar cell has led to an enhancement of the power conversion efficiency