Material and interface engineering for vacuum deposited perovskite solar cells

Resumen

The aim of this thesis was the development of materials and device architectures for the preparation of efficient vacuum deposited perovskite solar cells. The effect of different charge transport layers, interfacial materials and electrodes on the performance of perovskite solar cells was studied. Emphasis was placed on the importance of reducing non-radiative recombination within the perovskite and at the interfaces, which is the key to maintain high photovoltage in a solar cell. a novel approach to prepare mixed iodide-chloride perovskites, using three-source vacuum deposition technique, was presented. MAPbI3-xClx perovskite films showed a homogenous morphology and good crystallinity, and were hence used to fabricate thin-film diodes to examine the optoelectronic properties. Under illumination, the photovoltage was found to be larger as compared to pure iodide perovskite, reaching 1.13 V and a power conversion efficiency exceeding 16%. In forward bias, we detected intense electroluminescence with a quantum yield of 0.3%, similar to that of state-of-the-art evaporated MAPbI3 solar cells. The high quantum yield for electroluminescence together with the long photoluminescence lifetime suggests a reduction of the non-radiative recombination rate. The importance of the choice of suitable interfacial charge transport layers, electrodes, and their combinations, was highlighted in chapter 4. The MAPbI3 perovskite layer was deposited by dual source vacuum deposition. BCP, Liq and their combination were used as interlayers between the electron transport layer and the top electrode. We observed that BCP and Liq can lead to devices with high rectification, fill factor, and photovoltage. We also observed that the use of low work function metals, such as Ba, can be beneficial for the reduction of non-radiative recombination, although at the price of the device stability. In chapter 5, the optimization of the front contact in perovskite solar cells was investigated. As in chapter 4, the MAPbI3 perovskite film was deposited by dual source vacuum deposition. The hole transport layer which was used to fabricate the perovskite solar cells is TaTm. To ensure an ohmic contact between the TaTm layer and the ITO, an additional MoO3 layer was placed in between the two materials. The hole extraction properties of the MoO3/TaTm was evaluated by selectively annealing either MoO3 (prior to the deposition of TaTm) or the bilayer MoO3/TaTm (without pre-treatment on the MoO3), at temperature ranging from 60 °C to 200 °C. We observed that having TaTm deposited and annealed together with the MoO3 layer led to large improvement in fill factor (80%) and power conversion efficiency (> 18%) at any annealing temperature, with the best results obtained at 140 °C.