A new approach to simulation of limiting photoconversion efficiency of tandem solar cells

TL;DR

This paper introduces a new theoretical method to calculate the maximum photoconversion efficiency of tandem solar cells, considering radiative recombination, energy-dependent absorption, and temperature effects, aligning well with experimental data.

Contribution

The authors develop a novel approach that incorporates energy-dependent absorption and temperature effects to accurately predict efficiency limits of tandem solar cells.

Findings

Efficiency peaks with increasing subcells, then declines due to spectral narrowing.

Efficiency is higher under AM0 conditions due to lower heat dissipation.

Theoretical results closely match experimental and detailed balance calculations.

Abstract

We develop a new approach to calculate the obtainable limit of photoconversion efficiency of tandem solar cells (SCs) and applied it to SCs with both vertical and lateral designs at AM0 and AM1.5 conditions. To get the maximum efficiency, only radiative recombination has been considered using typical radiative recombination parameters of the direct band gap III-V semiconductors, and explicit energy dependence of light absorption. When simulating the efficiency, we selfconsistently took into account the fact that the amount of the heat dissipated by SC decreases as the number of current-matched sub-cells increases. As the operating SCs temperature decreases both the open-circuit voltage and the photoconversion efficiency increase. It is shown that the above effect is especially strong for SCs operating under AM0 conditions. As the number of subcells is increased, narrowing the spectral range for each subcell, the photocurrent is additionally reduced due to the energy dependent light absorption, the factor generally ignored in the standard approaches. Application of our formalism results in a maximum in the theoretical dependence of the efficiency on the number of subcells, which was indeed observed experimentally. Besides agreement with experiment, our theoretical results are also close to other efficiencies calculated using detailed balance based approaches.