A combined transient photovoltage and impedance spectroscopy approach for a comprehensive study of interlayer degradation in non-fullerene acceptor organic solar cells.

Adam Pockett,Wing C Tsoi,Harrison Ka Hin Lee,Matthew J Carnie,Brendan L Coles

doi:10.1039/c9nr02337b

Adam Pockett, Wing C Tsoi + Show 3 more

Open Access

https://doi.org/10.1039/c9nr02337b

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Abstract

Organic solar cells utilise thin interlayer materials between the active layer and metal electrodes to improve stability and performance. In this work, we combine transient photovoltage (TPV) and impedance spectroscopy (EIS) measurements to study how degradation affects both the active layer and the interlayer. We show that neither technique alone can provide a complete insight into both of these regions: TPV is more suited to studying degradation of the active layer; EIS clearly identifies the properties of the interlayer. By analysing both of these approaches we are able to assess how different interlayers impact the stability of the active layer, as well as how the interlayers themselves degrade and severely limit device performance. EIS measurements are also able to resolve the impact of the interlayer on series resistance even when it is not apparent from standard current-voltage (JV) measurements. The technique could therefore be valuable for the optimisation of all devices.

Highlights

Photovoltaic power production is dominated by silicon, a mature technology that has achieved many of the required milestones for successful commercialisation, namely high efficiency, low cost and excellent stability
We show that neither technique alone can provide a complete insight into both of these regions: transient photovoltage (TPV) is more suited to studying degradation of the active layer; electrochemical impedance spectroscopy (EIS) clearly identifies the properties of the interlayer
We show that TPV measurements are extremely useful in assessing the degradation of the active layer as a result of trap formation, while EIS measurements reveal more detail about the charge transport across the interlayer itself

Summary

Introduction

Photovoltaic power production is dominated by silicon, a mature technology that has achieved many of the required milestones for successful commercialisation, namely high efficiency, low cost and excellent stability. Perovskites are an exciting prospect, demonstrating high efficiencies and potential for low cost manufacture via solution processing. Relatively poor stability is a major obstacle to widescale deployment. Both of these technologies present concerns over the environmental impact of their manufacture. This pertains primarily to the energy intensive nature of high-quality silicon wafer production,[1,2] and toxicity issues related to the presence of lead in perovskites.[3,4]

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