Correlated In-Situ Low-Frequency Noise and Impedance Spectroscopy Reveal Recombination Dynamics in Organic Solar Cells using Fullerene and Non-Fullerene Acceptors

TL;DR

This study uses correlated low-frequency noise and impedance spectroscopy to analyze charge recombination and transport in organic solar cells with fullerene and non-fullerene acceptors, revealing differences in recombination dynamics and providing a diagnostic tool for material design.

Contribution

It introduces the first application of Kleinpenning model fitting to 1/f noise data in organic solar cells, linking noise characteristics to charge transport regimes and efficiency.

Findings

PDI-based OPVs exhibit higher recombination than fullerene-based ones.

1/f noise increases significantly under illumination, correlating inversely with efficiency.

Low-frequency noise spectroscopy effectively diagnoses charge transport in photovoltaic materials.

Abstract

Non-fullerene acceptors based on perylenediimides (PDIs) have garnered significant interest as an alternative to fullerene acceptors in organic photovoltaics (OPVs), but their charge transport phenomena are not well understood, especially in bulk heterojunctions (BHJs). Here, we investigate charge transport and current fluctuations by performing correlated low-frequency noise and impedance spectroscopy measurements on two BHJ OPV systems, one employing a fullerene acceptor and the other employing a dimeric PDI acceptor. In the dark, these measurements reveal that PDI-based OPVs have a greater degree of recombination in comparison to fullerene-based OPVs. Furthermore, for the first time in organic solar cells, 1/f noise data are fit to the Kleinpenning model to reveal underlying current fluctuations in different transport regimes. Under illumination, 1/f noise increases by approximately four orders of magnitude for the fullerene-based OPVs and three orders of magnitude for the PDI-based OPVs. An inverse correlation is also observed between noise spectral density and power conversion efficiency. Overall, these results show that low-frequency noise spectroscopy is an effective in-situ diagnostic tool to assess charge transport in emerging photovoltaic materials, thereby providing quantitative guidance for the design of next-generation solar cell materials and technologies.