Peak External Photocurrent Quantum Efficiency Exceeding 100% via MEG in a Quantum Dot Solar Cell

Abstract

Multiple exciton generation (MEG) is a process that can occur in semiconductor nanocrystals, or quantum dots (QDs), whereby absorption of a photon bearing at least twice the bandgap energy produces two or more electron-hole pairs. Here, we report on photocurrent enhancement arising from MEG in lead selenide (PbSe) QD-based solar cells, as manifested by an external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) that peaked at 114 ± 1% in the best device measured. The associated internal quantum efficiency (corrected for reflection and absorption losses) was 130%. We compare our results with transient absorption measurements of MEG in isolated PbSe QDs and find reasonable agreement. Our findings demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.

In situ measurement of exciton energy in hybrid singlet-fission solar cells

“…O f the options for renewable energy, photovoltaic techno logies [1][2][3] with the potential to exceed the ShockleyQueisser limit 4 on single bandgap devices are particularly attractive [5][6][7][8] . One strategy is to sensitize a low bandgap semicon ductor with a higher bandgap material that can generate additional photocurrent from absorbed high energy photons 6,9 .…”

“…One strategy is to sensitize a low bandgap semicon ductor with a higher bandgap material that can generate additional photocurrent from absorbed high energy photons 6,9 . Such an opportunity is offered by singlet fission, which is the spin conserving process by which a spin singlet exciton on an organic chromophore splits to form a pair of lower energy triplet excitons on neighbouring molecules 10 .…”

“…Alivisatos and co workers used nanocrystals in photovoltaics dispersed in polymer matrices 32 , and subsequent studies have investigated bilayer struc tures 33 and hybrid organic/inorganic junctions 34 . There has also been steady progress in lead chalcogenide nanocrystal solar cells in a variety of device architectures [5][6][7]35,36 . In spite of this progress, there is a broad recognition of the need for innovations in materials.…”

Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

“…[1][2][3] These solids consist of macroscopic arrays of colloidally synthesized nanoparticles, wherein the band gap and the electronic properties of the composite array can be tuned by varying the size 4 and surface chemistry 5 of the constitutive elements, respectively. However, colloidally synthesized nanocrystals typically exhibit low impurity concentrations, 6 requiring post-synthetic treatments to effectively dope the nanocrystal solid.…”

Nanoscale Effects in Water Splitting Photocatalysis

“…10). The MEG effect has been made responsible for the abnormally high efficiency of PbSe-sensitized TiO 2 photoelectrochemical cells [103] and PbSe photovoltaic cells [104].…”