Supersensitization of CdS quantum dots with a near-infrared organic dye: Toward the design of panchromatic hybrid-sensitized solar cells

The photoresponse of quantum dot solar cells (QDSCs) has been successfully extended to the near-IR (NIR) region by sensitizing nanostructured TiO2–CdS films with a squaraine dye (JK-216). CdS nanoparticles anchored on mesoscopic TiO2 films obtained by successive ionic layer adsorption and reaction (SILAR) exhibit limited absorption below 500 nm with a net power conversion efficiency of ∼1% when employed as a photoanode in QDSC. By depositing a thin barrier layer of Al2O3, the TiO2–CdS films were further modified with a NIR absorbing squaraine dye. Quantum dot sensitized solar cells supersensitized with a squariand dye (JK-216) showed good stability during illumination with standard global AM 1.5 solar conditions, delivering a maximum overall power conversion efficiency (η) of 3.14%. Transient absorption and pulse radiolysis measurements provide further insight into the excited state interactions of squaraine dye with SiO2, TiO2, and TiO2/CdS/Al2O3 films and interfacial electron transfer processes. The synergy of combining semiconductor quantum dots and NIR absorbing dye provides new opportunities to harvest photons from different regions of the solar spectrum.