Numerical and Experimental Investigation of Parabola-Cone Structured Films on Perovskite Solar Cells

Abstract

Global energy consumption has reached new peaks year on year and keeps increasing because of continuously growing demand. Solar energy is an abundant clean energy source, which has become one of the most promising energy sources to cope with potential energy crisis in the future as the solar cell technology keeps developing. There have been significant achievements in emerging photovoltaic research especially on efficiency and fabrication techniques of perovskite solar cell in recent years. However, there is still large proportion of incident light that remains unabsorbed due to optical losses before reaching the photoactive layer. This thesis will investigate a potential approach to enhance the light absorption in photoactive layer through numerical modelling and experimental fabrication with characterisation. The background and solar cell fundamentals are briefly introduced followed by a quick review of existing literature that is relevant to the absorption enhancement for solar cell. Based on review of previous and current research progress in solar cell absorption enhancement, the research objectives focus on the impact on optical absorption due to parabola-cone array at the front surface of perovskite solar cell using a finite-difference time-domain (FDTD) method with the aid of computational tool pack. To investigate the optical behaviour of perovskite solar cell with parabola-cone surface structure, parabolacone array is modelled on a perovskite solar cell surface with varying parameters such as height, base diameter, aspect ratio, angle of incidence and base duty ratio. The modelling results suggest that the aspect ratio and the base duty ratio of parabola-cone array are two key parameters that can affect the transmission and absorption of incident light. It was discovered that parabola-cone with aspect ratio of 1.0 and 1.5 are the two best performed geometry setup among the selected values under normal incidence when the base diameter of parabola-cone is around the absorption spectrum of the solar cell as they can provide the highest photo generation rate and short-circuit current density, which are important measure of solar cell’s optical absorption. The oblique incidence scenario is also modelled for a parabola-cone array to further investigate the enhancement effect. The modelling results show a nonlinear relationship between the angle of incidence and the short-circuit current density of a solar cell for solar cell with and without parabola-cone structured surface. For parabola-cone with base diameter of 1 um and base duty ratio of 1.0 under oblique incidence, it was discovered that the enhancement in short-circuit current becomes more distinctive as the aspect ratio increases from 0.5 to 2.0 especially for large incident angle, achieving an absorption enhancement of around 5% when the aspect ratio is 2.0. The direct-writing laser beam lithography and photo imprint lithography techniques are studied by fabricating the parabola-cone array with proposed geometric setup onto the front surface of a perovskite solar cell to explore the practicability of proposed fabrication techniques. The intended surface structure is characterised for geometrical profile as well as the solar cell performance, which is measured prior and after the parabola-cone structured film is applied. Results from both modelling and experiments are analysed and it is found that the fabricated structured film demonstrates strong absorption enhancement impact when the aspect ratio is 1.5 and base diameter of 1 um under normal incidence. The intended parabola-cone array can generally be achieved with proposed techniques however, there is still a lot of room for improvement especially in terms of accuracy for geometric profile. Overall, the fabricated parabola-cone achieved average 8% enhancement in short-circuit current density for selected angle of incidence, which improves the energy conversion efficiency up to 1% - 2% compared to solar cells with no surface structure, depending on the angle of incidence.