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# Stability-limiting heterointerfaces of perovskite photovoltaics

## Abstract

Optoelectronic devices consist of heterointerfaces formed between dissimilar semiconducting materials. The relative energy-level alignment between contacting semiconductors determinately affects the heterointerface charge injection and extraction dynamics. For perovskite solar cells (PSCs), the heterointerface between the top perovskite surface and a charge-transporting material is often treated for defect passivation1,2,3,4 to improve the PSC stability and performance. However, such surface treatments can also affect the heterointerface energetics1. Here we show that surface treatments may induce a negative work function shift (that is, more n-type), which activates halide migration to aggravate PSC instability. Therefore, despite the beneficial effects of surface passivation, this detrimental side effect limits the maximum stability improvement attainable for PSCs treated in this way. This trade-off between the beneficial and detrimental effects should guide further work on improving PSC stability via surface treatments.

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## Relevant articles

• ### Stability of 2D and quasi-2D perovskite materials and devices

Communications Materials Open Access 06 September 2022

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## Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

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## Acknowledgements

This work was supported by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office under award number DE-EE0008751. J.-W.L. acknowledges support from a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) (grant numbers 20214000000640, 20213030010400) and a POSCO Science Fellowship from the POSCO TJ Park Foundation. The TEM work at UC Irvine was supported by the National Science Foundation (NSF) under grant number DMR-2034738. Part of the computing resources used in this work were provided by the National Center for High-Performance Computing of Turkey (UHEM). Y.J.S. and J.-W.L. acknowledge support by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (grant numbers NRF-2022R1C1C1011975 and NRF-2021R1A2C2007141). N.-G.P. acknowledges financial support from NRF grants funded by MSIT under contract NRF-2021R1A3B1076723 (Research Leader Program). We acknowledge the use of facilities and instrumentation at the UC Irvine Materials Research Institute (IMRI), which is supported in part by the National Science Foundation through the UC Irvine Materials Research Science and Engineering Center (DMR-2011967). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract number DE-AC02-05CH11231. We thank M. E. Liao, K. Huynh, M. S. Goorsky, S. Nuryyeva, K. N. Houk, K.-H. Wei and B. Jeong for experimental assistance, measurements or discussions; and S. Shelton, Y. Liu and the Molecular Foundry for the third-party laboratory device efficiency measurements.

## Author information

Authors

### Contributions

S.T., T.H. and Y.Y. conceived the idea. S.T. and T.H. designed and conducted most of the experiments, supervised by Y.Y. T.W.Y., K.P., D.-K.L. and T.Y. performed the KPFM and AFM measurements and analysed the data, supervised by Y.J.S., J.-W.L. and N.-G.P. I.Y. did the theoretical calculations, modelling and data analysis. M.X. performed the STEM and EDX measurements and analysis, supervised by X.P. Q.X. performed the confocal PL mapping and part of the UPS measurements. C.-H.C., R.Z. and D.M. performed the chemical synthesis. Q.X. and K.P. assisted with experiments and film and device fabrication. R.W., Y.Z., H.-C.W., J.X. and J.-W.L. assisted with data analysis and discussion. S.T., T.H., R.W., J.-W.L. and Y.Y. wrote the manuscript, and all authors contributed feedback and commented on the manuscript.

### Corresponding authors

Correspondence to Rui Wang, Jin-Wook Lee or Yang Yang.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

## Peer review

### Peer review information

Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work.

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## Extended data figures and tables

### Extended Data Fig. 1 Morphology of the perovskite films.

Surface morphology of the: a, reference; b, OAI-treated; c, OATsO-treated; d, OATFA-treated; e, OABr-treated; and f, OABF4-treated perovskite films measured by SEM. All scale bars represent 2 μm. No obvious difference can be seen between the reference and treated perovskite films.

### Extended Data Fig. 2 Topography of the passivated perovskite films.

Representative 3D topography of the: a, OAI-treated; b, OABF4-treated; and c, OATsO-treated perovskite films measured by AFM. All scale bars represent 2 μm. d, Comparison of the height depth distribution of the films. Depth distribution histograms for the: e, OAI-treated; f, OABF4-treated; and g OATsO-treated perovskite films. Insets include the fitted statistical parameters. SD, standard deviation.

### Extended Data Fig. 3 Heterointerface energy band diagrams.

Schematic interpretation of the heterointerface band alignments of the a, OAI-treated and b, OATsO-treated devices under illumination in open-circuit condition. The band alignments are constructed based on the UPS and KPFM results. CBM, conduction band minimum; VBM, valence band maximum; $${E}_{{fn}}$$, electron quasi-fermi level; $${E}_{{fp}}$$, hole quasi-fermi level. The dashed gray lines in b indicate $${E}_{{fn}}$$ and $${E}_{{fp}}$$of the OAI-treated device from a. The diagrams are not drawn to scale. Both surface treatments create a type I energy alignment at the heterointerface, but the vacuum level upshift of the OATsO-treated device minimized the potential well to mitigate the electron accumulation.

### Extended Data Fig. 4 Device cross-sectional KPFM profiling.

a, CPD profile; b, KPFM spatial mapping; c, corresponding AFM spatial mapping; and d, electric field distribution of the OAI-treated device. e, CPD profile; f, KPFM spatial mapping; g, corresponding AFM spatial mapping; and h, electric field distribution of the OATsO-treated device. Measurements were performed under illumination in open-circuit condition. All scale bars represent 300 nm. The CPD offsets were adjusted such that the CPD value of the buffer layer becomes zero. Note that this does not affect the electric field and charge displacement profiles, which calculate the derivatives of the CPD profiles. Although we do not expect the rough morphology seen in c to affect the KPFM signal, we cannot completely rule this out at this stage. Therefore, we have repeated the KPFM measurement on another separate OAI-treated device. As shown in Supplementary Fig. 4, we were able to reproduce the potential drop at the perovskite/spiro-MeOTAD heterointerface.

### Extended Data Fig. 5 Device photovoltaic parameters.

Box plots showing the distribution of the: a, VOC; b, JSC; c, FF; and d, PCE of the devices. Centre line, median; box limits, 25th and 75th percentiles; whiskers, outliers.

### Extended Data Fig. 6 Characterization of the OATsO-treated devices.

a, Current density-voltage curves of the best-performing OATsO-treated device, in reverse scan (blue line) and forward scan (red line). Inset includes the measured photovoltaic parameters. b, EQE spectrum and integrated JSC of an OATsO-treated device. The integrated JSC is 24.6 mA cm−2, and therefore well matched (less than 3% discrepancy) with the measured value. c, Absorbance profile of an OATsO-treated film on glass measured by UV-Vis spectroscopy. Inset includes a Tauc plot and linear fits to estimate the optical bandgap.

### Extended Data Fig. 7 Third-party device performance measurements.

a, Current density-voltage curve, and b, box plot showing the PCE distribution of the encapsulated OATsO-treated devices. Measurements were performed at the Molecular Foundry, Berkeley, CA, USA. As the measurements were fully done in ambient air (RH approximately 50%), all devices had to be encapsulated, which resulted in a drop in performance. c, PCE evolution with time under lightsoaking of an encapsulated OATsO-treated device. Current density-voltage curves of the same device d, before and e, after the encapsulation procedure, measured in-house.

### Extended Data Fig. 8 Universality verification on a FAPbI3 composition.

a, UPS secondary electron cut-offs of the perovskite films. b, Steady-state and c, time-resolved PL spectra of the glass/perovskite films. d, Steady-state and e, time-resolved PL spectra of the glass/perovskite/spiro-MeOTAD films. The carrier lifetimes are fitted with a mono-exponential decay function. f, Box plots of the distribution of the device photovoltaic parameters. Centre line, median; box limits, 25th and 75th percentiles; whiskers, outliers. g, Current density-voltage curves and h, EQE spectrum and integrated JSC of the best-performing device treated with OATsO. The integrated JSC is 25.4 mA cm−2, well matched (approximately 3% discrepancy) with the measured scan value.

### Extended Data Fig. 9 Open-circuit stability test device performance.

Evolution with time of the normalized average a, Jsc, b, VOC, and c, FF of the devices under continuous illumination with a metal halogen lamp. The encapsulated devices were aged in ambient atmosphere at RH ~ 40% and T ~ 40 °C in open‐circuit condition. Error bars represent the standard deviation of four devices for each condition.

### Extended Data Fig. 10 Activation energy for halide migration.

ac, Energy profiles for the extra-lattice migration of a, bromine and b, iodine in a neutral uncharged or negatively charged environment, and c, corresponding activation energy barriers. df, Energy profiles for the intra-lattice migration of d, bromine and e, iodine in a neutral uncharged or negatively charged environment, and f, corresponding activation energy barriers.

## Supplementary information

### Supplementary Information

This file contains Supplementary Notes 1–10, Tables 1–7, Figs. 1–20 and References.

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Tan, S., Huang, T., Yavuz, I. et al. Stability-limiting heterointerfaces of perovskite photovoltaics. Nature 605, 268–273 (2022). https://doi.org/10.1038/s41586-022-04604-5

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• DOI: https://doi.org/10.1038/s41586-022-04604-5

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