Enhancing silicon solar cells with singlet fission: the case for Förster resonant energy transfer using a quantum dot intermediate

Stefan Wil Tabernig,Benjamin Daiber,Bruno Ehrler,Tianyi Wang

doi:10.1117/1.jpe.8.022008

Stefan Wil Tabernig, Benjamin Daiber + Show 2 more

Open Access

https://doi.org/10.1117/1.jpe.8.022008

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Abstract

One way for solar cell efficiencies to overcome the Shockley–Queisser limit is downconversion of high-energy photons using singlet fission (SF) in polyacenes like tetracene (Tc). SF enables generation of multiple excitons from the high-energy photons, which can be harvested in combination with Si. In this work, we investigate the use of lead sulfide quantum dots (PbS QDs) with a band gap close to Si as an interlayer that allows Förster resonant energy transfer (FRET) from Tc to Si, a process that would be spin-forbidden without the intermediate QD step. We investigate how the conventional FRET model, most commonly applied to the description of molecular interactions, can be modified to describe the geometry of QDs between Tc and Si and how the distance between QD and Si, and the QD bandgap affects the FRET efficiency. By extending the acceptor dipole in the FRET model to a 2-D plane, and to the bulk, we see a relaxation of the distance dependence of transfer. Our results indicate that FRET efficiencies from PbS QDs to Si well above 50% are possible at very short but possibly realistic distances of around 1 nm, even for QDs with relatively low photoluminescence quantum yield.

Highlights

The domination of the solar cell market by silicon led to the search of add-ons that could increase efficiency while maintaining low cost
We showed that Förster resonant energy transfer (FRET) from PbS quantum dot (QD) to silicon is possible with sufficiently high FRET efficiencies, even for QDs that have a bandgap close to silicon and low photoluminescence quantum yield (PLQY)
While efficient FRET is only possible over small separation distances in the order of a few nanometers, those distances are physically feasible, given careful engineering of the interface

Summary

Introduction

The domination of the solar cell market by silicon led to the search of add-ons that could increase efficiency while maintaining low cost. One possible way to increase efficiency is by downconverting high-energy light using an organic material that exhibits singlet fission (SF). In a single-junction solar cell, photons with energy above the bandgap can excite an electron into the conduction band. As the charge carriers quickly thermalize to the band edge. Downconversion schemes minimize the energy lost by thermalization, by converting high-energy photons to lower-energy charge carriers. Downconversion via SF can improve on the single-junction Shockley–Queisser[1,2] efficiency limit, raising it from 33.7% to 44.4%.3

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