Novel Materials and Deposition Techniques for Solution Processed Solar Cells

Whilst many advances have been made in the field of solution processed solar cells (SPSCs), there is still much work to be done if they are to fulfil their potential and reduce the cost of commercial photovoltaic devices. This thesis aims to assist in moving towards this objective by investigating ways to overcome some of the barriers to the commercialization of SPSCs. Such barriers include the costly and mechanically brittle electrode material of indium tin oxide, the use of solution deposition techniques which are not compatible with large-scale production, and a lack of understanding of the properties of promising new semiconducting materials such as organometal halide perovskites. In this work a novel indium-free multilayer semi-transparent electrode has been fabricated and incorporated as the anode in polymer solar cells. Whilst molybdenum oxide is typically used as the ‘seed layer’ material in such trilayer structures, its replacement with tellurium dioxide has been found to lead to an enhanced transmittance in the optimised electrodes and to an increased short circuit current when such electrodes are employed in polymer solar cells. The roll-to-roll compatible deposition technique of ultrasonic spray-coating has, for the first time, been successfully used for the fabrication of films of the organometal trihalide perovskite CH3NH3PbI3-xClx. Such films were subsequently successfully employed as the active layer in planar solar cells. This deposition technique is then extended to hole transporting and electron transporting materials in order to move towards a fully spray-deposited solar cell. Finally, a combination of structural investigation techniques have been employed to monitor the formation of the perovskite CH3NH3PbI3-xClx during thermal annealing of a precursor film. In-situ X-ray scattering measurements are used together with ex-situ scanning electron microscopy in order to correlate the evolution of the film during annealing to solar cell performance. In addition, the activation energy for the transition from precursor to perovskite has been calculated.