Halide perovskite solar cellsstrategies for high stability

Abstract

Among the most advanced emerging photovoltaic technologies, halide perovskite solar cells (PSCs) have evolved significantly in only a few years, achieving certified power conversion efficiencies (PCE) above 25%. However, some drawbacks of the technology that limits their commercialization are the presence of toxic Pb-based materials, limitations in the scale-up of the technology and most important, its long-term stability under continuous operation. Semiconductor oxides (including graphene oxide) have been employed as excellent barrier layers due to their low fabrication cost and ease of synthesis, but above all, due to the properties of stability and long life that provide to the final PSC device. In this thesis, we propose three strategies to overcome instability issues in PSCs: (a) additive engineering on the halide perovskite adsorbed (Chapter 2), (b) the fabrication of carbon-based PSCs (Chapter 3) and (c), the replacement of classical semiconductor oxides for ferroelectric oxides as transport layers (Chapter 4). I initiate the description of this work with a brief introduction to the topic of energy and perovskite solar cells (Chapter 1). The I present the three different strategies employed to enhance PSC stability. The first strategy, described in Chapter 2, includes the use of organic additives with phosphonate and carboxylic functional groups that are able to passive shallow point defects, resulting in ion immobilization and the enhancement of the PSC stability. The use of Carbon-based electrodes in PSC (Chapter 3) have demonstrated to improve moisture resistance and thus, overall solar cell performance. In this section, I will present the most recent results on the fabrication of complete PSCs applying carbon electrodes. Finally, I describe the work carried out on the replacement of classical semiconductor oxides applied in PSC as transport layers (such as TiO2 or SnO2), by ferroelectric oxides, especially Lead Zirconate Titanate (PZT) and Bismuth Ferrite (BFO). Initial studies with PZT have shown that the detrimental oxygen vacancies present in semiconductor oxides, which degrade the halide perovskite, are linked to the polarization properties in ferroelectric oxide and not to the photodegradation of the device. Finally, Chapter 5 and 6 describe the different methodologies employed in this thesis and the conclusion of the work, respectively.