Recent Progress of Electron Storage Mn Center in Doped Nanocrystals

Mn doping in semiconductor nanocrystals (NCs) has been reviewed for its unequivocal relevance to solar energy harvesting in terms of both mechanistic approaches of electron storage in the Mn center and improved power conversion efficiency (PCE). Mn-doped NCs have been measured to have significantly higher PCE than the undoped counterpart, which has been reviewed for a number of different host NCs including different alloy and core-shell structures. Such increment of PCE has been attributed to electron relaxation from the hot states of the host NCs via the Mn state (that occurs at hundreds of picosecond time scale) which acts as electron-storage center. This can avoid the detrimental charge recombination significantly, and at the same time, fast electron injection from the Mn state to TiO2 leads to enhancement of PCE performance. These phenomena are clearly demonstrated by analyzing the feedback from femtosecond transient absorption, time-resolved photoluminescence, and impedance spectroscopy.