Intense Internal and External Fluorescence as Solar Cells Approach the Shockley-Queisser Efficiency Limit

TL;DR

This paper explains how achieving high external fluorescence efficiency is crucial for solar cells to approach the Shockley-Queisser limit, emphasizing the importance of internal luminescence efficiency and optical design.

Contribution

It highlights the fundamental role of intense external and internal fluorescence in solar cells nearing theoretical efficiency limits, linking optical losses to device performance.

Findings

Efficient external fluorescence indicates low internal optical losses.

High internal luminescence efficiency (>90%) is necessary for optimal external emission.

External fluorescence efficiency is a key factor in approaching the Shockley-Queisser limit.

Abstract

Absorbed sunlight in a solar cell produces electrons and holes. But, at the open circuit condition, the carriers have no place to go. They build up in density and, ideally, they emit external fluorescence that exactly balances the incoming sunlight. Any additional non-radiative recombination impairs the carrier density buildup, limiting the open-circuit voltage. At open-circuit, efficient external fluorescence is an indicator of low internal optical losses. Thus efficient external fluorescence is, counter-intuitively, a necessity for approaching the Shockley-Queisser efficiency limit. A great Solar Cell also needs to be a great Light Emitting Diode. Owing to the narrow escape cone for light, efficient external emission requires repeated attempts, and demands an internal luminescence efficiency >>90%.