Photovoltaics has experienced an unprecedented growth over the last ten years. As in semiconductors, photovoltaic technology based on silicon solar cells has a combination of strengths that have made it difficult to displace as the mainstream photovoltaic material. However, as the efficiency of silicon solar cells is very close to the highest efficiency in theory and reduction in cost is slow, there is a pressing need for new technology that promises either significantly higher energy conversion efficiencies or significantly lower processing costs. The new emergence of the photovoltaic material, perovskite, is a promising star due to the rapid progress in its efficiency. In this thesis, we will focus on this newly emerged photovoltaic technology.

Firstly, we have introduced the fabric...[ Read more ]

Photovoltaics has experienced an unprecedented growth over the last ten years. As in semiconductors, photovoltaic technology based on silicon solar cells has a combination of strengths that have made it difficult to displace as the mainstream photovoltaic material. However, as the efficiency of silicon solar cells is very close to the highest efficiency in theory and reduction in cost is slow, there is a pressing need for new technology that promises either significantly higher energy conversion efficiencies or significantly lower processing costs. The new emergence of the photovoltaic material, perovskite, is a promising star due to the rapid progress in its efficiency. In this thesis, we will focus on this newly emerged photovoltaic technology.

Firstly, we have introduced the fabrication of perovskite materials and devices with the well-established industrial method, namely, reactive closed space sublimation. We have shown that the reactive closed space sublimation of perovskite has the potential to be large­-scale, with high-throughput and low-cost. In addition, we have achieved the highest efficiency of up to 16.2% in small area devices, whereas in large area devices, a relatively high efficiency (>14%) has also been demonstrated with good uniformity. Our results indicate that the reactive closed space sublimation method is quite suitable for the mass production of perovskite materials and devices.

Based on the reactive closed space sublimation process, a low temperature, fast, and reversible anion exchange reaction was observed in the metal-halide perovskite. Although processed in the solid-state phase, the exchanged hybrid perovskite showed good quality in terms of morphology conservation, phase transformation and homogenous composition. Furthermore, we found that the anion exchange reaction does not induce any remarkable defects resulting from the lattice transformation and morphology reconstruction. In some cases, the beneficial exchange of halide species involving simultaneous displacement reaction and crystallization can be used to improve the perovskite solar cell performance.

Moreover, we have identified that control of the perovskite morphology with a bilayer structure is crucial to achieve high efficiency perovskite solar cells. With better control over the perovskite morphology with a bi-layer structure in the device, a high efficiency of up to 15.2% was achieved even though the perovskite solar cells fabrication was wholly processed in ambient conditions with high humidity. In addition, the bi-layer structure also ensures high reproducibility for the perovskite solar cells.

Finally, we have explored the magnetron sputtering metal oxides as the charge transport layer in the perovskite solar cells. Particularly, SnO₂ and NiO_x have shown their potential as electron and hole transport layers in the perovskite solar cells, respectively. These inorganic metal oxide materials also demonstrated their ability in the improvement of the stability of the perovskite devices. Moreover, preliminary results of the mixed cation halide perovskite with inorganic Cs cation will also be presented as a useful way to further stabilize the perovskite materials and devices against ambient moisture.