The Effect of Metal Salt Passivation Layers on Perovskite PV Stability & Performance
Josephine Surel a, Pietro Caprioglio a, Akash Dasgupta a, Henry Snaith a
a The University of Oxford, Mansfield Road, United Kingdom
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
London, United Kingdom, 2023 June 12th - 14th
Organizers: Tracey Clarke, James Durrant and Trystan Watson
Poster, Josephine Surel, 274
Publication date: 30th March 2023

Though perovskite solar cells (PSCs) have continued to improve in performance in recent years, stability remains a significant challenge. One potential avenue to improve their stability is through the incorporation of passivation layers, which can enhance the electronic properties of the perovskite layer and reduce charge recombination at the interfaces. In this work, we present a study of the impact of commonly used metal salt passivation layers on the performance and stability of wide bandgap (1.8 eV) PSCs. We analyse the optical and electrical properties of the perovskite with various thicknesses of the passivation layers, as well as the device performance and stability under environmental stress. Our work focuses on understanding the dual effect of the passivation layers. We observed that, while some of these layers enhance PSCs' performance, they can also impact their stability. For example, adding a thin layer of metal salt between the perovskite and the electron transport layer (ETL) can improve the Voc of a 1.8 eV PSC from 1.24 in the control device to 1.30 V, but simultaneously reduce the stability. We observed that these passivated devices exhibit a PCE drop from 17.4% to 6% in only 18 hours under heat and light stress. To understand the mechanisms behind this degradation process, we coupled XRD, PLQY and QFLS mapping, charge extraction and fast-JV (hysteresis) measurements. Our results indicate that these metal salts can induce a localized degradation at the interface between perovskite and ETL, enhancing the negative effect of ionic migration and field screening. Additionally, we examine the trade-offs between performance and stability of a series of different metal salts implemented as passivation layers as well as within the perovskite layer itself in order to shed light on the effect of the single ions. Our aim is to understand the degradation pathway caused by these layers and to provide future strategies for the perovskite community in order to concomitantly achieve high-performing and stable PSCs. 

J. Surel acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the focus program SPP 2196.

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