Interface Engineering for Highly Efficient Perovskite Solar Cells

After decades of research, crystalline silicon technology dominates the global photovoltaic market by 92%. To gain market share from crystal silicon solar cells, emerging photovoltaic technologies have to demonstrate a combination of high power conversion efficiency (PCE), easy and cost-effective manufacturing processes and long-term stability. Recent researches suggest that organic-inorganic halide perovskites have the potential to meet these conditions and become competitive in the marketplace. The work presented here is comprised of an experimental study on the fabrication of perovskite solar cells using a two-step hybrid evaporation-spincoating method. Solution processing enables easy fabrication processes with possibility of band-gap tuning for tandem application while vacuum basted methods offer the advantages of deposition on non-planar surfaces like light trapping pyramidal textured structures, interesting for tandem configuration on high efficiency silicon solar cells. The hybrid two-step evaporation-spincoating deposition method, gains benefit from both solution processing and vacuum based deposition advantages while not suffering from the drawback of hazardous solvents consumption in solution processing. With maturing of the fabrication methods, a deepened understanding of which factors determine PCE, becomes more and more important for further improvements. Especially understanding of the crystallization and the layer ripening is crucial as those determine the occurring of defect centers that could limit performance. Accordingly, the role of excess PbI2 in perovskite structures and its impact on crystallization quality, optoelectronic properties and photovoltaic performance of different perovskite solar cells is studied in this thesis. It is found that a higher concentration of remnant and unconverted PbI2 correlates with smaller and stronger interconnected grains, as well as with an improved optoelectronic performance of the solar cells with higher efficiencies and the mitigation of hysteresis. Moreover, the issue of ''Interface Engineering'' at the perovskite top and bottom interfaces is addressed. Optimization of the charge carrier transport layers improved the optoelectronic and photovoltaic parameters. The impact of different transparent conductive oxides is also investigated in this thesis. The optical and electrical parameters of the perovskite absorber deposited on FTO and ITO transparent conductive oxides are compared. This is interesting especially for the tandem applications where the interface engineering is crucial for decreasing the parasitic losses. Tandem perovskite on silicon architecture is presented as an outlook for this thesis. Implementation of perovskite absorber fabricated by hybrid method atop highly efficient silicon bottom cell would lead to the efficiencies beyond theoretical efficiency limit of single junction solar cells.