Lead sulfide(PbS)quantum dots(QDs)exhibit a low,tunable band gap and a high absorption coefficient,establishing PbS QDs as a promising candidate for colloidal quantum dot(CQD)solar cells and allowing PbS CQD devices to deliver an unprecedented power efficiency of 8%.These types of solar cells consist of a compact/mesoporous TiO2 layer on a transparent conducting oxide (TCO),followed by a PbS QD layer deposited by spin coating/drop casting methods,and finally a thermally evaporated metal which serves as a back contact.In these devices,it is important to control the band gap as well the band position of the QDs to efficiently inject electrons into TiO2 and holes into the metal electrode.However,the similar energy levels present within the PbS QDs increase the probability of electron-hole recombination.
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