Beyond Shockley–Queisser: Molecular Approaches to High-Efficiency Photovoltaics

Abstract

Molecular materials afford abundant flexibility in the tunability of physical and electronic properties. As such, they are ideally suited to engineering low-cost, flexible, light-harvesting materials that break away from the single-threshold paradigm. Single-threshold solar cells are capable of harvesting a maximum of 33.7% of incident sunlight, whereas two-threshold cells are capable of energy harvesting efficiencies exceeding 45%. In this Perspective, we provide the theoretical background with which upper efficiency limits for various multiple-threshold solar cell architectures may be calculated and review and discuss various reports that employ processes such as triplet-triplet annihilation and singlet fission in multiple-threshold devices comprised of molecular materials.

Nature of ground and electronic excited states of higher acenes

“…Recently, with a growing interest in solar energy and solar cells, 4 and 5 have also been made into OPV devices (23)(24)(25)(26)(27). Furthermore, 3-5 have been shown to be able to undergo singlet fission (28)(29)(30)(31)(32)(33) ( 1 M* + 1 M → 2 3 M*), which in principle can raise the efficiency limit of a solar cell to more than 40% (34,35) by converting one high-energy singlet exciton to two spatially separated lower-energy triplet excitons.…”

Deuteration of Perylene Enhances Photochemical Upconversion Efficiency

“…7 One way to access and harness the energy of these below-bandgap photons is photochemical upconversion (UC) via triplet triplet annihilation (TTA). [8][9][10][11][12][13][14] Significant progress has been made in recent years to improve PV applications of UC, 8,[15][16][17][18][19] to develop integrated UC-PV devices, 20 and to better understand the underlying TTA process. [21][22][23][24][25] The process by which sub-bandgap photons can be reclaimed by UC is shown in Figure 1.…”

Increased upconversion performance for thin film solar cells: a trimolecular composition

“…These two devices have absorption onsets of 1.7 eV and 1.8 eV, respectively, making them ideal candidates for UC enhancement under AM1.5G illumination. 6–8 The combination of the dual-emitter UC system and the devices leads to record current enhancements. This UC architecture is similar to the mixed system reported by Cao et al , 32 who observed an increased quantum yield of a dual DPBF/DPA emitter system as compared to the individual components.…”

“…2–5 A maximum solar power conversion efficiency of around 43% has been calculated for an upconversion-assisted solar cell assuming the AM1.5G solar spectrum. 3,6–8 …”