Optimizing the Efficiency of Solar Photon Upconversion

Abstract

Low-energy photons, which are not used by a solar cell, can be converted to higher-energy photons by photon upconversion. The figure-of-merit of upconvertors, J UC , is given in mA cm −2 under 1 sun excitation conditions. A device-relevant J UC should not be less than 0.1 mA cm −2 . However, to date, the highest J UC reported is in the 10 −2 mA cm −2 range. In this Perspective, we analyze the shortcomings of previously reported devices and unfold a roadmap toward device-relevant, high-efficiency upconvertors.

Optimizing photon upconversion by decoupling excimer formation and triplet triplet annihilation

“…Triplet-triplet annihilation photon upconversion (TTA-UC) can help light harvesting materials to overcome their bandgap limitation and thus achieve higher solar energy conversion efficiencies beyond the Shockley-Queisser limit. [1][2][3][4][5][6][7] The mechanism has recently been successfully incorporated in solar cells, [8][9][10][11][12][13][14] photocatalysts, [15][16][17][18] optical devices, [19][20][21][22][23][24] and light imaging. [25][26][27][28][29][30][31] It requires two functional species, a sensitizer and an annihilator.…”

Ultrafast Charge Transfer and Upconversion in Zinc β‐Tetraaminophthalocyanine‐Functionalized PbS Nanostructures Probed by Transient Absorption Spectroscopy

“…This is reasonable given the large energy offset ( % 1eV) in electron states between the constituents,w hich greatly inhibits direct electron tunneling. II) Hole transfer is complete and only electron transfer contributes to the singlet bleach after 6ps, which we infer from the largely constant bleach of feature (2) in Figure 2a. Under these assumptions,w eg auge an upconversion efficiency on the order of 13 %.…”

“…[1] UC therefore bears great prospects for energy conversion by solar cells or water splitting,d isplay technologies as well as therapeutic applications such as bio-imaging and photodynamic radiotherapy. [2] UC for instance is observed in rareearth doped crystals,w here UC efficiencies of 24.2 %f or optimized single crystals and 7.6 %f or nanocrystals (NCs) have been reported. [3] Despite its indisputable success,U C with rare-earth elements also faces inherent challenges,s uch as concentration and/or surface quenching, [4] and mitigating these effects by searching for alternative UC materials is potentially very rewarding.O ne alternative is to utilize undoped compound semiconductor NCs like CdSe,P bSe and PbS as sensitizers in conjunction with organic semiconductor molecules (OSC) as emitters.…”

All-optical augmentation of solar cells using a combination of up- and downconversion

“…17 The accepted figure of merit for an upconverting solar cell is the enhancement of short-circuit current density due to upconversion, corrected for any solar concentration, ΔJ UC . 18,19 The highest ΔJ UC so far reported for crystalline silicon cells is 8.9 × 10 −3 mA∕cm 2 , 20 representing a 0.55% relative increase in solar cell efficiency.…”