| Description |
In 2009, CH3NH3PbI3 was integrated into a photovoltaic cell for the first time, starting the meteoric rise of metal halide perovskites (MHPs). Three-dimensional MHPs have earned the reputation as the future of photovoltaics because of its large absorption coefficients, long carrier diffusion length, defect tolerance, and high carrier mobility. However, the Achilles heel of 3D MHPs is their intrinsic and extrinsic lack of stability, i.e., degrading due to light and water exposure. Low dimensional MHPs share many of thefantastic properties of their 3D counterparts, while also providing significantly better structural stability. The same metal halide network that is the foundation of 3D MHPs can be reorganized into 2D (quantum well), 1D (quantum wire), or 0D (quantum dot) structures, through careful choice of organic cation. By reducing the dimensionality of the MHP lattice, fascinating optoelectronic features, such as high exciton binding energy and anisotropic charge transport, are accessible. Low dimensional MHPs have rich modularity through a more flexible tool box of possible organic cation that is easily accessible due to the lack of spatial constraints that 3D MHPs crystal lattice requires. With the exceptional modularity of low dimensional MHPs comes a host of optoelectronic properties that have yet to be explored. This dissertation adds to the growing body of knowledge on these materials through fundamental investigations of exciton binding energy, phase change, bandgap, carrier type, phase heterogeneity, and charge transfer characteristics. We used a host of steady state, biased (temperature and voltage), and transient optical techniques paired with detailed structural characterization to relate orientation, optical properties, and morphology together. In the 2D quantum well MHP (BA)2PbI4, electroabsorption (EA) was used, for the first time, to observe Franz-Keldysh oscillations which determined the bandgap of the material. In the quasi-2D (BA)2(MA)n-1PbnI3n+1 (n = 2-4) quantum well series, EA clearly elucidated multiple phases, and their respective topical features, that coexisted in a heterogeneous thin film. Lastly, we investigated the charge transfer dynamics of 1D (NDIC2)Pb2I6 heterojunctions. From these studies, accurate optoelectronic properties have been determined, which allows for low dimensional MHPs to be integrated into high efficient photovoltaic device architectures. |
