A perspective of mesoscopic solar cells based on metal chalcogenide quantum dots and organometal-halide perovskites (2013)

We review two types of inorganic nanomaterials—metal chalcogenide quantum dots (QDs) and lead halide perovskites—that serve as prospective light harvesters in hybrid mesoscopic solar cells. Metal chalcogenide QDs are introduced in three parts: chalcogenides of cadmium (CdS, CdSe and CdTe), chalcogenides of lead (PbS and PbSe) and chalcogenides of antimony (Sb2S3 and Sb2Se3). The devices made using these chalcogenide QDs in a liquid-type electrolyte showed the best cell efficiencies, ranging from 3 to 6%. For solid-state QD-sensitized solar cells (QDSCs), the device performances were generally poor; only devices made of Sb2S3 and PbS QDs attained cell efficiencies approaching ∼7%. In contrast, nanocrystalline lead halide perovskites have emerged since 2009 as potential photosensitizers in liquid-type sensitized TiO2 solar cells. In 2012, the efficiencies of the all-solid-state perovskite solar cells were enhanced to 9.7 and 10.9% using anodes of TiO2 and Al2O3 films, respectively, with 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (spiro-OMeTAD) as a hole-transporting material. In 2013, the performance of a TiO2 solar cell sensitized with lead iodide perovskite (CH3NH3PbI3) was optimized further to attain an overall power conversion efficiency η=15%, which is a new milestone for solar cells of this type having a device structure similar to that of a dye-sensitized solar cell. In light of growing energy demands, the depletion of fossil fuels and the damaging environmental effects of their use, efficient energy generation from renewable sources must be attained. Because of the abundance of solar energy, photovoltaic devices have attracted a great deal of attention as they offer a promising solution to contemporary energy challenges. Eric Wei-Guang Diau and co-workers from the National Chiao Tung University in Taiwan review recent research progress on two types of inorganic photosensitizers for mesoscopic solar cells: metal chalcogenide MmXn quantum dots — where M represents cadmium, lead or antimony and X denotes sulfur, selenium or tellurium — and organometal halide perovskite nanocrystals, which contain halogens rather than the oxygens of conventional perovskites. In mesoscopic solar cells, these materials serve as light-harvesting layers where capture and charge separation occur. Diau and co-workers summarize their synthesis, characterization and photovoltaic properties and introduce their recent progress trends on device performance for all-solid-state solar cells. Metal chalcogenide quantum dots (QDs) and lead halide perovskites are two types of prospective light harvesters for mesoscopic solar cells. The two most promising QD sensitizers are PbS and Sb2S3, for which the PCEs of their corresponding QDSCs have attained ∼7% in 2012. In 2013, the performance of a TiO2 solar cell sensitized with lead-iodide perovskite (CH3NH3PbI3) was optimized to attain an overall power conversion efficiency of 15%, which is a new milestone for solar cells of this type, with a device structure similar to that of a dye-sensitized solar cell.