Theory of solar cell light trapping through a nonequilibrium Green's function formulation of Maxwell's equations

Abstract

We develop a theory of solar cell light trapping based on directly solving Maxwell's equations through a non-equilibrium Green's function formalism. This theory rigorously connects the maximum power absorbed by the solar cell to the density of states of the cell. With this theory we are able to reproduce all standard results in solar cell light trapping previously derived using approximate formalisms. Therefore our development places solar cell light trapping theory on a much firmer theoretical foundation. Moreover, here the maximum power formula is derived without the assumption of reciprocity, unlike all previous theories on solar cell light trapping. Therefore, we prove that the upper bound of light trapping enhancement cannot be overcome with the use of non-reciprocal structures. As a numerical test, we simulate an absorber structure that consists of a non-reciprocal material, and show that the absorption enhancement factor is largely independent of non-reciprocity, in consistency with the theory.

From Solar Cells to Ocean Buoys: Wide-Bandwidth Limits to Absorption by Metaparticle Arrays

“…As was also emphasized in Ref. 10, the result also applies to linear nonreciprocal systems, since the density of states of transposed-related materials is the same (G (r, r) = G t t (r, r) [13]). Here for simplicity, we consider a reciprocal system in the derivation.…”

“…This is an alternative to the derivation in Ref. 10, which differs in that it directly uses the reciprocity (or generalized reciprocity) from Maxwell's equations. As was also emphasized in Ref.…”

“…In this paper, we obtain approximate broad-band/angle absorption limits for a case in which the traditional Yablonovitch result is not useful: dilute arrays of "metaparticles"(synthetic absorbers/scatterers). Known limits bound the absorption at every wavelength [9,10], but they tend to be loose when considering large bandwidths since coherent effects average out [5,11]. Here, we find limits on the absorption for arrays of particles that can be described by the radiative-transfer equation (RTE) [12,13].…”

“…This allows us both to obtain analytical upper bounds (Eqs. 7,10) and identify the ideal operating regime of absorbing metaparticle arrays.…”

Photoexcited charge carrier behaviors in solar energy conversion systems from theoretical simulations

“…In combination of the Keldysh NEGF and SCF theory, quantum transport calculations could be done, for example, by the nanoDCAL distribution . The manual for nanoDCAL is very helpful.…”