Research paper: Bulk Passivation of Lead Halide Perovskites: The Key to High-Performance Indoor Photovoltaics at Very Low-Light Intensities

Summary

This study investigates the crucial role of bulk passivation in enhancing the performance of lead halide perovskite (LHP) indoor photovoltaics (IPVs) under very low-light intensities (≤200 lux), conditions rarely assessed despite their prevalence in indoor environments. The main goal was to evaluate sodium thioglycolate (STG) as a bifunctional bulk passivator in a triple-cation LHP precursor solution. Key findings show that STG incorporation significantly improves IPV performance at low-light intensities (100 and 200 lux), driven by enhancements in fill factor (FF) and open-circuit voltage (VOC). For instance, at 200 lux, STG-passivated devices achieved an average PCE of 22.21%, a 6% enhancement over reference devices (20.99%). This improvement is attributed to reduced trap-assisted recombination, accelerated charge extraction, and increased ion migration resistance, confirming effective bulk trap passivation by STG. XPS analysis confirmed STG's interaction with LHP, passivating Pb2+-based defects. At higher intensities (1000 lux), efficiency improvements were negligible, underscoring the specific benefit for low-light conditions.

Why it matters

These findings are crucial for the advancement of indoor photovoltaics, particularly for powering the rapidly expanding Internet of Things (IoT) devices, which require efficient operation under diverse and often very dim indoor lighting. By demonstrating the critical role of bulk trap passivation, especially at low light levels, this research offers a pathway to mitigate performance losses (FF and VOC) and reduce leakage currents caused by defects. This work provides significant guidance for designing more efficient and robust LHP-based IPVs, essential for real-world applications and encouraging a shift towards assessing IPV performance under realistic low-illumination conditions.

How Fluxim tools used

The Paios platform from Fluxim AG was extensively used for crucial electrical characterisation. Specifically, transient photovoltage (TPV) and transient photocurrent (TPC) measurements were performed using Paios. These measurements were vital to confirm the suppressed nonradiative recombination and accelerated charge extraction in the STG-passivated IPVs. Paios allowed for the precise acquisition of decay data, showing faster TPC decay for STG-passivated devices (indicating more effective charge extraction) and delayed TPV decay (supporting reduced trap-assisted recombination). Furthermore, electrochemical impedance spectroscopy (EIS) was also carried out using the Paios platform, enabling detailed analysis of charge carrier dynamics, ion migration, and confirmation of increased recombination resistance and accelerated charge transfer. The ability of Paios to perform these comprehensive transient and impedance measurements provided direct evidence supporting the effectiveness of STG bulk passivation.

Publication Details

Karpiola, E., Grandhi, G.K., Doyranli, C., Han, Y., Alexander, A., Jagadamma, L.K., Tewari, A., Manna, D. and Vivo, P. (2025), Bulk Passivation of Lead Halide Perovskites: The Key to High‐Performance Indoor Photovoltaics at Very Low‐Light Intensities. Solar RRL, 11: 2500195. https://doi.org/10.1002/solr.202500195