Characterizing Fill Factor Limitations in Perovskite-Silicon Tandem Solar Cells

TL;DR

This paper investigates the mechanisms limiting fill factor in perovskite-silicon tandem solar cells and proposes strategies to mitigate these losses, aiming to improve overall efficiency.

Contribution

It introduces a methodology to analyze fill factor losses, highlighting the impact of photoshunt and other factors, and suggests strategies to overcome these limitations.

Findings

Photoshunt reduces fill factor under illumination in perovskite cells.

Over-illumination of the bottom cell can hide photoshunt effects.

Strategies to mitigate photoshunt can improve tandem cell performance.

Abstract

Perovskite-silicon tandem technology has exceeded the single junction theoretical efficiency limit. However, there is still distance to the thermodynamic limit mainly caused by the fill factor. This work presents a methodology to illustrate the mechanisms of FF loss in perovskite-Si monolithic tandem solar cells. Apart from the series resistance related loss characterized by electroluminescence, another loss factor is from the photoshunt, a phenomenon in which the parallel resistance apparently reduces under illumination in perovskite solar cells due to the moderate charge transport layer mobility. In addoition, the two-diode property of the Si cell can also influence the FF of tandem devices. The photoshunt can be hidden when the bottom cell is over illuminated, which explains highly efficient tandem solar cells are usually bottom cell limited. This work outlines strategies that overcoming the photoshunt issue can move the perovskite top cell closer to low FF losses in tandem solar cells.