Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices1,2. This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively3) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects4. Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance5, perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance6. The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions7 and with local strain8, both of which make devices less stable9. Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process10,11, we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices.
|Number of pages||7|
|Publication status||Published - 2020 Apr 16|
Bibliographical noteFunding Information:
Acknowledgements T.A.S.D. acknowledges support of a National University of Ireland (NUI) Travelling Studentship. The work received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement no. 756962). A.J.W., S.K., V.P., C.E.P., E L.W., J.M., M.K.L.M. and K.M.D. acknowledge that this work was supported by the Femtosecond Spectroscopy Unit of the Okinawa Institute of Science and Technology Graduate University. The authors acknowledge the support for this work from the Imaging Section and Engineering Support Section of the Okinawa Institute of Science and Technology Graduate University. This work was supported by JSPS KAKENHI Grant Number JP19K05637. S.M. acknowledges funding from the Summer Fellowship Programme of the Japan Society for the Promotion of Science and from a UK Engineering and Physical Sciences Research Council (EPSRC) studentship. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). We thank Diamond Light Source and beamline scientists J. Parker, P. Quinn, M. Danaie and T. Slater for access and support in use of beamline I14 (proposal nos. sp19023-1 and sp19023-2) and the electron Physical Science Imaging Centre (ePSIC instrument E02 and proposal nos. EM19793-1, EM19793-2) that contributed to the results presented here. F.U.K. thanks the Jardine Foundation and Cambridge Trust for a doctoral scholarship. P.A.M. thanks the EPSRC for financial support under grant no. EP/R008779/1. E.M.T. acknowledges funding from the EPSRC under grant reference EP/ R023980/1 and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 841265. S.D.S. and E.M.T. acknowledge funding from the EPSRC grant "Centre for Advanced Materials for Integrated Energy Systems (CAM-IES)" EP/P007767/1 and Cambridge Royce facilities grant EP/ P024947/1. M.A. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie actions grant agreement no. 841386. Y.-H.C. acknowledges support of a Cambridge Trust-Taiwan scholarship. M.A.-J. thanks Cambridge Materials Limited, Wolfson College, University of Cambridge, and EPSRC (grant no. EP/M005143/1) for their funding and technical support. Z.A.-G. acknowledges funding from a Winton Studentship and an ICON Studentship from the Lloyd’s Register Foundation. This work was supported by a National Research Foundation of Korea grant funded by the Korean government (MSIT) (no. 2018R1C1B6008728).
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
All Science Journal Classification (ASJC) codes