Hydroxamic acid pre-adsorption raises the efficiency of cosensitized solar cells

Dye-sensitized solar cells (DSCs) convert light into electricity using photosensitizers adsorbed on the surface of nanocrystalline mesoporous titanium dioxide (TiO2) films along with electrolytes or solid charge-transport materials1-3. They possess many features including transparency, multicolor and low-cost fabrication, and are being deployed in glass facades, skylights and greenhouses4. Recent development of sensitizers5-10, redox mediators11-13 and device structures14 has improved the performance of DSCs, particularly under ambient light conditions14-17. To further enhance its efficiency, it is pivotal to control the assembly of dye molecules on the surface of TiO2 that favors charge generation. Here, we report a route of pre-adsorbing a monolayer of a hydroxamic acid derivative on the surface of TiO2 to improve the dye molecular packing and photovoltaic performance of two newly-designed co-adsorbed sensitizers that harvests light quantitatively across the entire visible domain. The best performing cosensitized solar cells exhibited a power conversion efficiency (PCE) of 15.2% (independently confirmed 15.2%) under standard air mass 1.5 global simulated sunlight, and showed long-term operational stability (500 hours). Devices with a larger active area of 2.8 cm2 exhibited PCE of 28.4 % to 30.2 % over a wide range of ambient light intensities along with high stability. Our findings pave the way for facile access to high performance DSCs and offer promising prospects for applications as power supply and battery replacement for low-power electronic devices18-20 that use ambient light as their energy source.