Beschreibung:
Abstract: Perovskite solar cells (PSCs) are gaining increasing importance and attention in the last decade. Even though high conversion efficiencies have been reached, one of the major bottlenecks for the commercialization of PSCs is their stability. Issues at the interfaces in the multilayered PSC architecture are suspected to be the significant contributor in causing low stability. <br><br>This doctoral thesis focusses on the analysis of various interfaces present in PSCs and traces methods to improve them. The investigation of individual interfaces is performed by developing suitable sub-cells, i.e., comprising only the particular interface of interest. Various optical and structural characterisation methods are used to determine layer and interface properties. After this step, complete devices are manufactured from the sub-cells, and their final performance is investigated to conclude the role and optimization of the interfaces. <br><br>The thesis accounts for the analysis of the interfacial quality of different n-i-p perovskite solar cells configurations, being based on hole-transport-layer (HTL)/Au or HTL-free/carbon-graphite (CG) electrodes. In particular, the former has been developed in a 6-month study exchange in Commonwealth Scientific and Industrial Research Organisation (CSIRO), Melbourne, Australia, and the latter developed throughout three years at Fraunhofer ISE. This peculiarity of working with various perovskite solar cell architecture gives this work a broad and comprehensive overview of the role of interfaces, particularly when all the layers are processed in-room ambient. <br><br>Three different types of interfaces were studied using suitable sub-cell configurations, and complete devices investigated thereafter. <br><br>1.Firstly, a cell architecture involving slot-die coated SnO2 as an electron transport layer (ETL) was used to investigate the quality of the ETL/perovskite interface in a PSC. For this purpose, an ITO/SnO2/perovskite sub-cell was used. UV treatment of the SnO2/perovskite interface led to an improved device stability attributed to the passivation effect by excess PbI2. This improvement resulted in retaining 80 % of the initial PCE value after 14 h of continuous AM 1.5 G illumination. <br><br>2.Various hole blocking layer (HBL) processing techniques were used to identify the quality and the role of the HBL in preventing recombination at the FTO/perovskite interface in a PSC. The layers were investigated through dark lock-in thermography (DLIT). An FTO/c-TiO2/ µ-graphite sub-cell was used for this purpose. The results showed that atomic layer deposition (ALD) of TiO2 allows to fabricate pin-hole free, shunt free HBLs, thereby reducing the recombination at the FTO/perovskite interface and achieving photo-voltages greater than 900 mV. <br><br>3.Thirdly, the role of the spacer layer in preventing recombination at the mp ETL/cathode interface for an HTL-free PSC architecture was investigated. For the first time, sputtered Al2O3 with thickness in the range of 10 – 100 nm was analyzed. FTO/c-TiO2/ mp-TiO2/Al2O3 sub-cell was used for quality analysis. The results showed that an ultra-thin 40 nm sputtered Al2O3 is sufficient to prevent the recombination at the mp-TiO2/carbon-graphite (CG) interface. A stable photo-voltage of 1 V and power conversion efficiency (PCE) of 12.1 % was achieved. Thereby, a double-mesoscopic architecture for PSC has been introduced. <br><br>The thesis shows that developing suitable sub-cells allows to investigate the quality of the various interfaces of PSCs individually and thus to understand their role in device stability. Finally, the findings from the sub-cell analysis are compared with the performance of complete devices to verify their significance. Thereby, methods to improve the interfaces can be found to achieve higher device efficiencies without compromising its stability