@phdthesis{Fischer2023,
  author    = {Fischer, Mathias},
  title     = {Transient Phenomena and Ionic Kinetics in Hybrid Metal Halide Perovskite Solar Cells},
  doi       = {10.25972/OPUS-32220},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-322204},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {The fact that photovoltaics is a key technology for climate-neutral energy production can be taken as a given. The question to what extent perovskite will be used for photovoltaic technologies has not yet been fully answered. From a photophysical point of view, however, it has the potential to make a useful contribution to the energy sector. However, it remains to be seen whether perovskite-based modules will be able to compete with established technologies in terms of durability and cost efficiency. The additional aspect of ionic migration poses an additional challenge. In the present work, primarily the interaction between ionic redistribution, capacitive properties and recombination dynamics was investigated. This was done using impedance spectroscopy, OCVD and IV characteristics as well as extensive numerical drift-diffusion simulations. The combination of experimental and numerical methods proved to be very fruitful. A suitable model for the description of solar cells with respect to mobile ions was introduced in chapter 4.4. The formal mathematical description of the model was transferred by a non-dimensionalization and suitable numerically solvable form. The implementation took place in the Julia language. By intelligent use of structural properties of the sparse systems of equations, automatic differentiation and the use of efficient integration methods, the simulation tool is not only remarkably fast in finding the solution, but also scales quasi-linearly with the grid resolution. The software package was released under an open source license. In conventional semiconductor diodes, capacitance measurements are often used to determine the space charge density. In the first experimental chapter 5, it is shown that although this is also possible for the ionic migration present in perovskites, it cannot be directly understood as doping related, since the space charge distribution strongly depends on the preconditions and can be manipulated by an externally applied voltage. The exact form of this behavior depends on the perovskite composition. This shows, among other things, that experimental results can only be interpreted within the framework of conventional semiconductors to a very limited extent. Nevertheless, the built-in 99 potential of the solar cell can be determined if the experiments are carried out properly. A statement concerning the type and charge of the mobile ions is not possible without further effort, while their number can be determined. The simulations were applied to experimental data in chapter 6. Thus, it could be shown that mobile ions make a significant contribution to the OCVD of perovskite solar cells. j-V characteristics and OCVD transients measured as a function of temperature and illumination intensities could be quantitatively modeled simultaneously using a single global set of parameters. By the simulations it was further possible to derive a simple experimental procedure to determine the concentration and the diffusivity of the mobile ions. The possibility of describing different experiments in a uniform temperaturedependent manner strongly supports the model of mobile ions in perovskites. In summary, this work has made an important contribution to the elucidation of ionic contributions to the (photo)electrical properties of perovskite solar cells. Established experimental techniques for conventional semiconductors have been reinterpreted with respect to ionic mass transport and new methods have been proposed to draw conclusions on the properties for ionic transport. As a result, the published simulation tools can be used for a number of further studies.},
  subject      = {Simulation},
  language  = {en}
}
@phdthesis{Armer2023,
  author    = {Armer, Melina Brigitte Melanie},
  title     = {High-Quality Lead-Free Double Perovskite Single Crystals and their Optical Properties},
  doi       = {10.25972/OPUS-32750},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327503},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {The presented thesis deals with the investigation of the characteristic physical properties of lead-free double perovskites. For this purpose lead-free double perovskite single crystals were grown from solution. In order to assess the influence of growth temperature on tail states in the material, the crystals were studied using Photoluminescence Excitation (PLE) and Transmission measurements. Additionally, lead-free double perovskite solar cells and thin films were investigated to address the correlation of precursor stoichiometry and solar cell efficiency. In a last step a new earth abundant lead-free double perovskite was introduced and its physical properties were studied by photoluminescene and absorptance. Like this it was possible to assess the suitability of this material for solar cell applications in the future.},
  subject      = {Perowskit},
  language  = {en}
}
@phdthesis{Hoecker2022,
  author    = {H{\"o}cker, Julian Harald},
  title     = {High-quality Organolead Trihalide Perovskite Crystals: Growth, Characterisation, and Photovoltaic Applications},
  doi       = {10.25972/OPUS-25859},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-258590},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Overview of the Organolead Trihalide Perovskite Crystal Area Studies of perovskite single crystals with high crystallographic quality is an important technological area of the perovskite research, which enables to estimate their full optoelectronic potential, and thus to boost their future applications [26]. It was therefore essential to grow high-quality single crystals with lowest structural as well as chemical defect densities and with a stoichiometry relevant for their thin-film counterparts [26]. Optoelectronic devices, e.g. solar cells, are highly complex systems in which the properties of the active layer (absorber) are strongly influenced by the adjacent layers, so it is not always easy to define the targeted properties and elaborate the design rules for the active layer. Currently, organolead trihalide perovskite (OLTP) single crystals with the structure ABX3 are one of the most studied crystalline systems. These hybrid crystals are solids composed of an organic cation such as methylammonium (A = MA+) or formamidinium (A = FA+) to form a three-dimensional periodic lattice together with the lead cation (B = Pb2+) and a halogen anion such as chloride, bromide or iodide (X = Cl-, Br- or I-) [23]. Among them are methylammonium lead tribromide (MAPbBr3), methylammonium lead triiodide (MAPbI3), as well as methylammonium lead trichloride (MAPbCl3) [62, 63]. Important representatives with the larger cation FA+ are formamidinium lead tribromide (FAPbBr3) and formamidinium lead triiodide (FAPbI3) [23, 64]. Besides the exchange of cations as well as anions, it was possible to grow crystals containing two halogens to obtain mixed crystals with different proportions of chlorine to bromine and bromine to iodine, as it is shown in Figure 70. By varying the mixing ratio of the halogens, it was therefore possible to vary the colour and thus the absorption properties of the crystals [85], as it can be done with thin polycrystalline perovskite films. In addition, since a few years it is also doable to grow complex crystals that contain several cations as well as anions [26, 80, 81]. These include the perovskites double cation - double halide formamidinium lead triiodide - methylammonium lead tribromide (FAPbI3)0.9(MAPbBr3)0.1 (FAMA) [26, 80] and formamidinium lead triiodide - methylammonium lead tribromide - caesium lead tribromide (FAPbI3)0.9(MAPbBr3)0.05(CsPbBr3)0.05 (CsFAMA) [81], which have made a significant contribution to increase the power conversion efficiency (PCE) in thin-film photovoltaics [47, 79, 182]. The growth of crystals to this day is performed exclusively from solution [23, 26, 56, 62]. Important preparation methods are the cooling acid-based precursor solution crystallisation [22], the inverse temperature crystallisation (ITC) [62], and the antisolvent vapour-assistant crystallisation (AVC) [137]. In the cooling crystallisation, the precursor salts AX and PbX2 are dissolved in an aqueous halogen-containing acid at high temperatures [56]. Controlled and slow cooling finally results in a supersaturated precursor solution, which leads to spontaneous nucleation of crystal nuclei, followed by subsequent crystal growth. The ITC method is based on the inverse or retrograde solubility of a dissociated perovskite in an organic solvent [23, 64]. With increasing temperature, the solubility of the perovskite decreases and mm-sized crystals can be grown within a few hours [23]. In the AVC method, the precursors are also dissolved in an organic solvent as well [137]. By slow evaporation of a so-called antisolvent [137], the solubility of the perovskite in the now present solvent mixture decreases and it finally precipitates. In addition, there are many other methods with the goal of growing high quality and large crystals in a short period of time [60, 61, 233, 310].},
  subject      = {Perowskit},
  language  = {en}
}
@phdthesis{Kiermasch2020,
  author    = {Kiermasch, David},
  title     = {Charge Carrier Recombination Dynamics in Hybrid Metal Halide Perovskite Solar Cells},
  doi       = {10.25972/OPUS-20862},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-208629},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {In order to facilitate the human energy needs with renewable energy sources in the future, new concepts and ideas for the electricity generation are needed. Solar cells based on metal halide perovskite semiconductors represent a promising approach to address these demands in both single-junction and tandem configurations with existing silicon technology. Despite intensive research, however, many physical properties and the working principle of perovskite PVs are still not fully understood. In particular, charge carrier recombination losses have so far mostly been studied on pure films not embedded in a complete solar cell. This thesis aimed for the identification and quantification of charge carrier recombination dynamics in fully working devices under conditions corresponding to those under real operation. To study different PV systems, transient electrical methods, more precisely Open-Circuit Voltage Decay (OCVD), Transient Photovoltage (TPV) and Charge Extraction (CE), were applied. Whereas OCVD and TPV provide information about the recombination lifetime, CE allows to access the charge carrier density at a specific illumination intensity. The benefit of combining these different methods is that the obtained quantities can not only be related to the Voc but also to each other, thus enabling to determine also the dominant recombination mechanisms.The aim of this thesis is to contribute to a better understanding of recombination losses in fully working perovskite solar cells and the experimental techniques which are applied to determine these losses.},
  subject      = {Solarzelle},
  language  = {en}
}
@article{HarkinBrochSchrecketal.2016,
  author    = {Harkin, David J. and Broch, Katharina and Schreck, Maximilian and Ceyman, Harald and Stoy, Andreas and Yong, Chaw-Keong and Nikolka, Mark and McCulloch, Ian and Stingelin, Natalie and Lambert, Christoph and Sirringhaus, Henning},
  title     = {Decoupling charge transport and electroluminescence in a high mobility polymer semiconductor},
  series = {Advanced Materials},
  volume    = {28},
  journal   = {Advanced Materials},
  number    = {30},
  doi       = {10.1002/adma.201600851},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-187670},
  pages     = {6378-6285},
  year      = {2016},
  abstract  = {Fluorescence enhancement of a high-mobility polymer semiconductor is achieved via energy transfer to a higher fluorescence quantum yield squaraine dye molecule on 50 ps timescales. In organic light-emitting diodes, an order of magnitude enhancement of the external quantum efficiency is observed without reduction in the charge-carrier mobility resulting in radiances of up to 5 W str\(^{-1}\) m\(^{-2}\) at 800 nm.},
  language  = {en}
}