Efficient CdSe Quantum Dot-Sensitized Solar Cells Prepared by an Improved Successive Ionic Layer Adsorption and Reaction Process

In pursuit of efficient quantum dot (QD)-sensitized solar cells based on mesoporous TiO2 photoanodes, a new procedure for preparing selenide (Se2−) was developed and used for depositing CdSe QDs in situ over TiO2 mesopores by the successive ionic layer adsorption and reaction (SILAR) process in ethanol. The sizes and density of CdSe QDs over TiO2 were controlled by the number of SILAR cycles applied. After some optimization of these QD-sensitized TiO2 films in regenerative photoelectrochemical cells using a cobalt redox couple [Co(o-phen)32+/3+], including addition of a final layer of CdTe, over 4% overall efficiencies were achieved at 100 W/m2 with about 50% IPCE at its maximum. Light-harvesting properties and transient voltage decay/impedance measurements confirmed that CdTe-terminated CdSe QD cells gave better charge-collection efficiencies and kinetic parameters than corresponding CdSe QD cells. In a preliminary study, a CdSe(Te) QD-sensitized TiO2 film was combined with an organic hole conductor, spiro-OMeTAD, and shown to exhibit a promising efficiency of 1.6% at 100 W/m2 in inorganic/organic hybrid all-solid-state cells.