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 TiO ₂ 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) ₃^2+/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.