Prospects for efficient solar energy upconversion using metalloporphyrins as dual absorber-upconverters

The novel potential use of selected metalloporphyrins as dual absorber-upconverters in solar photovoltaics is discussed. Additional efficiencies are available if use can be made of the porphyrin's short-lived S2 state, which is formed directly by excitation in the strong Soret transition in the blue-violet and also by absorption in the Q bands followed by rapid intersystem crossing and upconversion by triplet-triplet annihilation. The main challenge in realizing a working photovoltaic based on such a protocol is that energy must be extracted from the S2 state of the porphyrin within its picosecond lifetime. The structure-property relationships that may be used to select metalloporphyrins with the longest possible intrinsic lifetimes are outlined. The prospects for energy extraction from S2via ultrafast electron transfer or ultrafast resonant electronic energy transfer within a solid structure designed to maximize efficiency are discussed. Both MOF and pendant porphyrin polymer structures offer reasonable possibilities.