Abstract
Heavy metal-based quantum dots (QDs) have been demonstrated to behave as efficient sensitizers in QD-sensitized solar cells (QDSSCs), as attested by the countless studies and encouraging efficiencies reported so far. However, their intrinsic toxicity has arisen as a major issue for the prospects of commercialization. Here, we examine the potential of environmentally friendly zinc copper indium sulfide (ZCIS) QDs for the fabrication of liquid-junction QDSSCs by means of photoelectrochemical measurements. A straightforward approach to directly adsorb ZCIS QDs on TiO2 from a colloidal dispersion is presented. Incident photon-to-current efficiency (IPCE) spectra of sensitized photoanodes show a marked dependence on adsorption time, with longer times leading to poorer performances. Cyclic voltammograms point to a blockage of the channels of the mesoporous TiO2 film by the agglomeration of QDs as the main reason for the decrease in efficiency. Photoanodes were also subjected to the ZnS treatment. Its effects on electron recombination with the electrolyte are analyzed through electrochemical impedance spectroscopy and photopotential measurements. The corresponding results bring out the role of the ZnS coating as a barrier layer in preventing electron leakage toward the electrolyte, as argued in other QD-sensitized systems. The beneficial effect of the ZnS coating is ultimately reflected in the power conversion efficiency of complete devices, reaching values of 2%. In a more general vein, through these findings, we aim to call the attention to the potentiality of this quaternary alloy, virtually unexplored as a light harvester for sensitized devices.
Highlights
In the last few decades, concerns about the unavoidable collapse of the current fossil fuel economy have prompted the development of a wide variety of technologies aimed to convert solar energy into electricity in a cost-effective way
In a more general vein, the overall correspondence between the results reported in this work and those obtained for colloidal CdSe-sensitized devices clearly reflects generalities in the importance of obtaining both an accurate control of interfaces in QDsensitized solar cells (QDSSCs) and a high level of understanding of these devices
A straightforward procedure for the direct adsorption of zinc copper indium sulfide (ZCIS) quantum dots (QDs) at mesoporous TiO2 films is described, offering a convenient alternative to the linker-mediated attachment reported for this sensitizer so far
Summary
In the last few decades, concerns about the unavoidable collapse of the current fossil fuel economy have prompted the development of a wide variety of technologies aimed to convert solar energy into electricity in a cost-effective way. Among the third generation solar cells, currently under development, the so-called sensitized solar cells are drawing a lot of attention.[1,2,3] The prospects of scalable and low cost fabrication via solution processing, together with their encouraging conversion efficiencies, make them promising candidates for feasibly exploiting solar energy. It must be noted that very recently hybrid inorganic–organic perovskites have been coupled to nanostructured oxides yielding outstanding performances, though their role as sensitizers is still under discussion.[6,7] Dye-sensitized solar cells have delivered impressive efficiencies of up to 12.3%,8 whereas the performance of QD-sensitized solar cells lags far behind these values.[9,10] the stunning properties of QDs, such as the tunable band gap, high extinction coefficient, and the unparalleled prospect of multiple exciton generation (MEG) still leave room for improvement.[11,12]
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