Device physics of colloidal quantum dot solar cells

This thesis focuses on the device physics of PbS QDs in electronic devices and the fabrication and optimisation of solar cells with various structures. Chapter 2 focuses on the fabrication of tandem solar cells featuring PbS QDs in combination with a blend of P3HT and PCBM. We successfully introduce a new Al/WO3 interlayer to fabricate tandem solar cells with an efficiency of ~2%, utilizing a broad absorption range. In Chapter 3 we present the use of PbS QDs with a thin shell of CdS as an alternative strategy for trap passivation. We observe increased VOC in Schottky solar cells, and show that this is due to a reduction of the trap density near the conduction band. Chapter 4 is devoted to the study of the temperature dependent properties of PbS solar cells and films. We fabricate p-n junction solar cells with an efficiency of ~9% and measure the temperature dependent behaviour. We observe increased efficiency at lower temperatures, particularly due to increased VOC and FF, without degradation of the JSC. We explain this trend by measuring the temperature dependence of the most important film properties, and give some guidelines for further enhancement of the solar cell efficiency at room temperature. Finally, in Chapter 5 we demonstrate a method to dope EDT-capped PbS films by altering the Pb/S ratio on the PbS surface. We find that p-n junction solar cells demonstrate higher JSC and FF, with approximately equal VOC, leading to improved overall efficiency. The reason for this is traced back to an increased doping concentration of the EDT-capped PbS film.