Multiple exciton generation in quantum dots versus singlet fission in molecular chromophores for solar photon conversion

Abstract

Both multiple exciton generation (MEG) in semiconductor nanocrystals and singlet fission (SF) in molecular chromophores have the potential to greatly increase the power conversion efficiency of solar cells for the production of solar electricity (photovoltaics) and solar fuels (artificial photosynthesis) when used in solar photoconverters. MEG creates two or more excitons per absorbed photon, and SF produces two triplet states from a single singlet state. In both cases, multiple charge carriers from a single absorbed photon can be extracted from the cell and used to create higher power conversion efficiencies for a photovoltaic cell or a cell that produces solar fuels, like hydrogen from water splitting or reduced carbon fuels from carbon dioxide and water (analogous to biological photosynthesis). The similarities and differences in the mechanisms and photoconversion cell architectures between MEG and SF are discussed.

Recent advances in energy transfer in bulk and nanoscale luminescent materials: from spectroscopy to applications

“…Concerning the mechanisms of improved PCE and short circuit current in the solar cells, it is quite easy to accept that the upconverted photons from the NIR part of solar radiation contribute dominantly to the enhanced performance. 255 According to the calculations made by Nozik et al, 256 the maximum PCE increases from 33.7% to 45% for a single band QD-based PV device under AM 1.5G illumination. This is why monochromatic laser has to be used as the excitation source to generate UC emission for the RE activated systems, rather than non-coherent light sources such as Xe-lamp and natural light.…”

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S1 (21Ag-) State of Pi-Conjugated Systems

“…In synthetic molecular materials developed for organic electronics they have transformed transistor and lightemitting diode technology [6][7][8] , as well as becoming promising components for next-generation photovoltaic (PV) devices with the potential to overcome the Shockley-Queisser limit via singlet fission (SF). In SF the absorption of a single photon ideally results in the formation of two spatially separated triplet excitons [9][10][11][12] , although a concerted sequence of ultrafast electronic and vibrational dynamics must compete with both radiative and non-radiative losses for this exciton multiplication to be efficient enough for applications [13][14][15][16][17] . Observation, understanding and control of these many-body quantum dynamics is therefore essential for optimisation of conjugated molecules for technologies such as SFenhanced PVs [18][19][20][21] .…”

Tuning Intramolecular Förster Resonance Energy Transfer and Activating Intramolecular Singlet Fission

“…The efficient utilization of high-energy photons represents one of the major challenges with regard to the optimization of third-generation photovoltaics.I nr ecent years,d own-converting high-energy excitons into am ultiple of low-energy excited states has emerged as ap romising strategy.T ot his end, singlet exciton fission (SF) is the molecular strategy to accomplish multiexciton generation (MEG). [1] SF is am any-body,s pin-conserving conversion phenomenon in organic materials;as inglet exciton 1 (S 1 S 0 )i st ransformed via ap air of triplet excitons 1 (T 1 T 1 ), often also referred to as the multiexcitonic state,i nto two independent triplet excited states 2 3 (T 1 ). [2] Thei nitial 1 (S 1 S 0 )t o 1 (T 1 T 1 ) interconversion is af orm of fast internal conversion, conserves spin, and is shown to proceed on (sub)picosecond timescales.I nc ontrast, the subsequent 2 3 (T 1 )f ormation involves achange in spin multiplicity and, in turn, represents the slow intersystem crossing (ISC) component of SF.…”