Periodic Reporting for period 1 - iSLIP-NMR (In Situ Light Irradiated Perovskite NMR)
Berichtszeitraum: 2021-04-01 bis 2023-03-31
Generating cheap, renewable energy is one of the greatest challenges currently facing society, to move away from fossil fuels and minimise further climate change. Perovskite solar cells are one of the forerunning future technologies to reduce the cost of solar energy, but they currently suffer from degradation under environmental conditions, preventing commercialisation. This objective of this project was to develop methodology to study hybrid perovskite materials, especially degradation and the mode of operation of different additives and treatments to improve stability. Specifically, the project focussed on nuclear magnetic resonance (NMR) spectroscopy, which yields detailed information about the atomic-scale structure, since it is this atomic-scale structure that determines the stability and performance of perovskite solar cells.
The project has resulted in six peer-reviewed publications by the end of the funding period, the results of which are described below. The results have also been disseminated at eight national and international conferences.
Studying surface coatings on hybrid perovskite thin films is limited by the extremely low sample mass. Dynamic nuclear polarization (DNP) is a technique to dramatically improve the sensitivity of NMR experiments. In this project, the challenges preventing application of DNP to perovskites were overcome, which enabled the NMR spectrum to be measured for a 20 nm surface coating on a single perovskite thin film (10.1021/jacs.2c05316). This showed that the additive adopted a layered perovskite structure, but exhibited significantly greater disorder than a bulk layered perovskite. This disorder is important to consider when developing structure–activity relationship for perovskite surface treatments. The researcher further applied these DNP methods in a collaborative project on another important class of materials, core–shell nanoparticles grown by chemical atomic layer deposition, to deduce the mechanism by which the shell nucleates (10.1021/jacs.1c12538). How this shell forms was an important unanswered question in the field and required the sensitivity and atomic-scale picture afforded by DNP NMR.
The cation dynamics in hybrid perovskites play a role in the excellent optoelectronic properties for solar cell applications. In this project, new methodology was developed to measure the rotation about each axis of the cation in various mixed cation perovskites (10.1021/jacs.7b04930). This provides the community with definitive experimental data to inform theory and calculations.
This project also involved collaboration on three application-focussed perovskite projects, where NMR was used to determine the local structure of cutting-edge perovskite systems with different treatments/additives, to reveal their method of operation. (1) A record open-circuit voltage was achieved for a perovskite solar cell by treating with neopentylammonium chloride. The researcher used NMR to show that this was achieved by the passivation of the surface by the treatment (10.1021/acsenergylett.1c02431). (2) The efficiency and stability of both pure iodide and mixed iodide–bromide perovskite solar cells were greatly improved by treatment with alkyldimethylammonium amphiphiles. The researcher used NMR to demonstrate the interaction of these species with the perovskite surface, supporting ab initio calculations to distinguish the effect of different analogues (10.1016/j.joule.2022.11.013). (3) Photo-induced halide segregation is one of the major issues for 3D mixed-halide perovskites. Greater stability against segregation was demonstrated for layered 2D mixed-halide perovskites, which the researcher demonstrated arises from intrinsic halide heterogeneity in the pristine materials (10.1021/acsenergylett.3c00160).
Studying surface coatings on hybrid perovskite thin films is limited by the extremely low sample mass. Dynamic nuclear polarization (DNP) is a technique to dramatically improve the sensitivity of NMR experiments. In this project, the challenges preventing application of DNP to perovskites were overcome, which enabled the NMR spectrum to be measured for a 20 nm surface coating on a single perovskite thin film (10.1021/jacs.2c05316). This showed that the additive adopted a layered perovskite structure, but exhibited significantly greater disorder than a bulk layered perovskite. This disorder is important to consider when developing structure–activity relationship for perovskite surface treatments. The researcher further applied these DNP methods in a collaborative project on another important class of materials, core–shell nanoparticles grown by chemical atomic layer deposition, to deduce the mechanism by which the shell nucleates (10.1021/jacs.1c12538). How this shell forms was an important unanswered question in the field and required the sensitivity and atomic-scale picture afforded by DNP NMR.
The cation dynamics in hybrid perovskites play a role in the excellent optoelectronic properties for solar cell applications. In this project, new methodology was developed to measure the rotation about each axis of the cation in various mixed cation perovskites (10.1021/jacs.7b04930). This provides the community with definitive experimental data to inform theory and calculations.
This project also involved collaboration on three application-focussed perovskite projects, where NMR was used to determine the local structure of cutting-edge perovskite systems with different treatments/additives, to reveal their method of operation. (1) A record open-circuit voltage was achieved for a perovskite solar cell by treating with neopentylammonium chloride. The researcher used NMR to show that this was achieved by the passivation of the surface by the treatment (10.1021/acsenergylett.1c02431). (2) The efficiency and stability of both pure iodide and mixed iodide–bromide perovskite solar cells were greatly improved by treatment with alkyldimethylammonium amphiphiles. The researcher used NMR to demonstrate the interaction of these species with the perovskite surface, supporting ab initio calculations to distinguish the effect of different analogues (10.1016/j.joule.2022.11.013). (3) Photo-induced halide segregation is one of the major issues for 3D mixed-halide perovskites. Greater stability against segregation was demonstrated for layered 2D mixed-halide perovskites, which the researcher demonstrated arises from intrinsic halide heterogeneity in the pristine materials (10.1021/acsenergylett.3c00160).
Hybrid perovskites are one of the most promising technologies to bring down the cost of solar energy. This is a key requirement to reduce dependence on fossil fuels and combat climate change. The research has made significant progress in methodology to understand degradation processes in hybrid perovskites, as well as the mode of operation of treatments and additives. The most significant progress beyond the state of the art is the application of dynamic nuclear polarization to perovskites to enable the observation of a surface coating on a single perovskite thin film. Moreover, through collaborative projects, the project has resulted in direct improvements to perovskite solar cell technologies. The methods developed here can be used to understand the degradation processes in hybrid perovskites, to enable stable perovskite solar cells and cheap solar energy.