Manuel Kober-Czerny

Abstract:

In this thesis, several different optoelectronic techniques are used to investigate the transient behaviour of photo-generated charge carriers in metal halide perovskites. The overarching objective is to gain a greater understanding of the fundamental properties of both three-dimensional and layered perovskite structures. The first two chapters introduce the field of research of metal halide perovskites for photovoltaic applications and provide the theoretical background necessary to evaluate the results presented in this thesis. All experimental methods used throughout the entire thesis are described in detail in the third chapter so that the results can be replicated.

Chapter four discusses the difficulties of measuring charge carrier mobilities with precision, with an emphasis on the role played by early-time recombination and exciton formation. The lateral, long-range charge carrier mobilities of different perovskite thin films are then reliably determined by performing transient photo-conductivity measurements and simulating a transient free-carrier fraction. The findings highlight the impact of the fabrication route on the long-range optoelectronic properties of the resulting thin films.

The fundamental properties of two-dimensional layered perovskites are investigated in Chapter five. The sum of the electron and hole mobilities for PEA2PbI4 and related two-dimensional perovskites are estimated using the approach described in the prior chapter. For PEA2PbI4, a remarkable long-range mobility of 8.0 ± 0.6 cm2 V−1 s−1 is found. This tenfold improvement in mobility over a typical 3D perovskite demonstrates the potential single-crystal-like charge transport properties of 2D polycrystalline thin films.

In the final chapter, an exciting, novel approach for analysing time-resolved photo-luminescence data is presented, by making use of Bayesian inference and a Markov-Chain Monte-Carlo algorithm. Using a FAPbI3 thin film as a case study, a number of parameters, including diffusion, and recombination constants can be accurately inferred. The findings provide new perspectives on the physics underlying observed optoelectronic properties. For some of the systems illustrated in this chapter, for instance, the distinction between surface and bulk appears to be less clear than previously assumed. Validation of the method is provided by comparisons to other experimental data, such as intensity-dependent PLQE and transient photo-conductivity.

Overall, this thesis contributes powerful analytical tools that can be applied to future studies of a wide range of metal halide perovskites.