AbstractsEngineering

Organic-inorganic hybrid solar cells such as dye-sensitized solar cells (DSSCs) have reached photovoltaic conversion efficiency of 12.3%.¹ Their immediate successor, perovskite solar cells (PSCs), have reached an unprecedented efficiency of 17.9% in 2014, from 3.81% in 2009 ², making them competitive with thin-film silicon based PV technology. However, the most significant concern for the organic-inorganic solar cells is their long-term instability, especially at high temperature, above ca. 60 °C, and in contact with moisture present in the air. Their application will be limited unless they have credited stability performance. Improving the stability of organic-inorganic solar cells and understanding their degradation mechanisms is essential for their commercialization and wide-spread use. In the thesis, the stability and degradation mechanisms of two types of organic-inorganic solar cells: flexible dye-sensitized solar cells (DSSCs) built on ITO/PEN substrates and perovskite solar cells (PSCs) were investigated. The first chapter was a general introduction to the organic-inorganic hybrid solar cells, especially dye-sensitized solar cells and perovskite solar cells, such as the development history, structure and operating principles of the cells and the research objectives of the studies. In Chapter 2, literatures regarding the stability of DSSCs and PSCs were thoroughly reviewed and findings of their degradation mechanisms were summarized, which also pointed out research gaps and critical stability issues that still need to be understood and improved. In Chapter 3, all the experimental details are specified, including the chemicals, materials, device fabrication and characterization techniques, stability testing conditions and data analysis. In Chapter 4, the characteristics of flexible DSSCs with the photoanode produced using cold isostatic pressing technique were studied using electrochemical impedance spectroscopy (EIS). The data obtained were analyzed using a transmission line model of DSSCs, which pointed out that the pressing technique may improve short term performance of the devices, but the long-term performance of devices made on plastic substrates deteriorated with aging as a result of reduced TiO₂ particle-particle and/or particle-conductive substrate contacts. The results obtained from Chapter 4 gave rise to the inspiration of the studies in Chapter 5, where the mechanical and electrochemical stability of compressed photoanodes (TiO₂/ITO/PEN) and counter electrodes (Pt/ITO/PEN) in three different ionic liquid (IL) based electrolyte environment were studied using mechanical bending machine, cyclic voltammetry (CV), EIS, X-ray photoelectron spectroscopy and Inductively coupled plasma mass spectrometry. The results showed that the presence of Li⁺ ions and H₂O molecules in the electrolyte were detrimental to the stability of devices. Li⁺ ions were responsible to the detachment of Pt particles from the Pt/ITO/PEN electrode and the increase in the recombination resistance of compressed TiO₂ films, explaining…