Figure 11(a) shows the schematic illustration of the working principle and configuration of typical QDSSCs. Similar to dye sensitized solar cell (DSC), QDSSCs consist of a QD sensitized photoelectrode and a counter electrode separated by a liquid electrolyte. In general, wide bandgap metal oxide (, ZnO, and ; in the following is used as an example) nanostructures [such as nanoparticulate, nanorods, nanowires (NWs), nanotubes, and inverse opal] are used as the photoelectrodes in QDSSCs. QDs can be deposited on the photoelectrodes by two kinds of in-situ growth methods, i.e., chemical bath deposition (CBD) and successive ionic layer absorption and reaction (SILAR), and by adsorption of presynthesized QDs through direct adsorption or linker-assisted QD deposition method.25,92–94 The in-situ deposition methods lead to high loading of QDs, but it is difficult to precisely control the QD size distribution, and surface trap state density in the QDs is high. For the presynthesized QD deposition method, the QDs are size-controlled and high-quality with low surface trap states, but normally the QD loading was low (14%) and thus the PCE was as low as .95 However, recently, Zhong’s group developed a method to increase the QD loading up to 34%, which leads to the highest record PCE of QDSSCs of 11.6%.87 This is comparable to the record PCE of DSC (11.9%).91 A number of QDs, such as CdS, CdSe, CdTe, PbS, , , CdSeTe, and core–shell structure or double layered QDs, such as CdSe/CdTe, ZnTe/CdSe, CdS/CdSe, PbS/CdS, have been applied as sensitizers in QDSSCs.25 Aqueous polysulfide solution is most widely used as the electrolyte for QDSSCs. Some solid-state hole transport materials (HTMs), such as P3HT, Spiro-OMeTAD, and CuSCN, are also used as hole scavenging and transport layers in QDSSCs.96–98 For the polysulfide electrolyte, copper sulfide () is the most used counter electrode. For the solid-state HTMs, gold and silver are commonly used as electrodes.