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

Dye-sensitized solar cells (DSCs) convert light into electricity by using photosensitizers adsorbed on the surface of nanocrystalline mesoporous titanium dioxide (TiO₂) films along with electrolytes or solid charge-transport materials^1-3. They possess many features including transparency, multicolour and low-cost fabrication, and are being deployed in glass facades, skylights and greenhouses⁴. Recent development of sensitizers^5-10, redox mediators^11-13 and device structures¹⁴ has improved the performance of DSCs, particularly under ambient light conditions^14-17. To further enhance their efficiency, it is pivotal to control the assembly of dye molecules on the surface of TiO₂ to favour 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 harvest light quantitatively across the entire visible domain. The best performing cosensitized solar cells exhibited a power conversion efficiency of 15.2% (which has been independently confirmed) under a standard air mass of 1.5 global simulated sunlight, and showed long-term operational stability (500 h). Devices with a larger active area of 2.8 cm² exhibited a power conversion efficiency 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 supplies and battery replacements for low-power electronic devices^18-20 that use ambient light as their energy source.