Abstract
Halide perovskites have emerged as leading candidates for next-generation solar cells and other photovoltaic applications. The power conversion efficiency of perovskite solar cells has already surpassed 25%, exceeding that of commercial silicon-based solar cells while having several times smaller fabrication costs. Their advantages also extend to very high tunability of colour and other properties.
When we began the perovskite study in 2018, the understanding of perovskite photophysics had been lagging behind the rapid development of their synthesis and solar cell efficiency via trial and error. Thus, our objective was to investigate the charge carrier dynamics in perovskites by using ultrafast pump-probe techniques. However, the traditional data analysis models were unable to explain the transient absorption signals we had obtained. It had been a common assumption in the research community that only photoinduced changes in absorption give rise to the signal, but we discovered that instead, the photoinduced changes in reflectance could also be a major factor. Whereas the samples in the past had been solutions or films with low refractive index, the new perovskites were instead thin-film samples with high refractive index, which boosts their reflectance. Therefore, to analyse the signal, we had to employ transient reflectance spectroscopy, but it was a rare technique and the available analysis tools were not intended for our case.
The objectives of this study became twofold: 1) establish new transient reflectance models for perovskite analysis, and 2) use them to acquire new information on perovskite photophysics. This approach led to several discoveries, such as evidence of non-ambipolar charge carrier diffusion and signals correlating with perovskite sample quality. It also provided knowledge of key carrier dynamics in greater detail than before, such as the charge trapping and the hot-carrier behaviour. Many of these results have practical implications for future perovskite devices, and some of the findings dispute popular theories in the literature.
When we began the perovskite study in 2018, the understanding of perovskite photophysics had been lagging behind the rapid development of their synthesis and solar cell efficiency via trial and error. Thus, our objective was to investigate the charge carrier dynamics in perovskites by using ultrafast pump-probe techniques. However, the traditional data analysis models were unable to explain the transient absorption signals we had obtained. It had been a common assumption in the research community that only photoinduced changes in absorption give rise to the signal, but we discovered that instead, the photoinduced changes in reflectance could also be a major factor. Whereas the samples in the past had been solutions or films with low refractive index, the new perovskites were instead thin-film samples with high refractive index, which boosts their reflectance. Therefore, to analyse the signal, we had to employ transient reflectance spectroscopy, but it was a rare technique and the available analysis tools were not intended for our case.
The objectives of this study became twofold: 1) establish new transient reflectance models for perovskite analysis, and 2) use them to acquire new information on perovskite photophysics. This approach led to several discoveries, such as evidence of non-ambipolar charge carrier diffusion and signals correlating with perovskite sample quality. It also provided knowledge of key carrier dynamics in greater detail than before, such as the charge trapping and the hot-carrier behaviour. Many of these results have practical implications for future perovskite devices, and some of the findings dispute popular theories in the literature.
| Original language | English |
|---|---|
| Place of Publication | Tampere |
| Publisher | Tampere University |
| ISBN (Electronic) | 978-952-03-2107-9 |
| ISBN (Print) | 978-952-03-2106-2 |
| Publication status | Published - 2021 |
| Publication type | G5 Doctoral dissertation (articles) |
Publication series
| Name | Tampere University Dissertations - Tampereen yliopiston väitöskirjat |
|---|---|
| Volume | 475 |
| ISSN (Print) | 2489-9860 |
| ISSN (Electronic) | 2490-0028 |
