OKASH UR REHMAN, MUHAMMAD (2025) IMPROVING THE EFFICIENCY AND OPERATIONAL STABILITY OF DMSO-FREE Sn PEROVSKITE SOLAR CELLS. [Tesi di dottorato]

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Abstract

Worldwide modern society is significantly dependent on energy from fossil fuels. The increasing impacts of climate change require a rapid and substantial decrease in greenhouse gas emissions and shift toward clean renewable energy sources. Among those solar energy is a more sustainable and affordable source to fulfil the global energy demands. However, solar energy efficiently requires the development of advanced materials for highly efficient photovoltaic (PV) system. Among other technologies, perovskite solar cells (PSCs) have seen remarkable advancements due to their remarkable photovoltaic properties. However, the constituent metal lead (Pb) is recognised as one of the most toxic elements to both the environment and human health. Tin perovskite solar cells (Sn-PSCs) have emerged as a promising eco-friendly alternative to toxic lead-based counterparts due to their appropriate bandgap adjacent to the Shockley-Queisser, low exciton binding energy and enhanced charge carrier mobility. Despite the fast crystallization, and oxidation of Sn²⁺ to the unwanted Sn⁴⁺ remains an obstacle towards better device performance. Here, to address this issue we show some strategies to enhance the efficiency and stability of the Sn perovskite through a dimethyl sulfoxide (DMSO) free fabrication route which is casing the Sn²⁺ oxidation. Interface engineering has emerged as a powerful method to enhance charge extraction and obtain optimum energy alignment in PSCs. To fabricate pinholes free absorption layer phenylethylammonium iodide (PEAI) was introduced at the bottom interface of the perovskite in conjunction with the hole-selective contact. As a result, we successfully achieved a champion PCE of 7.9% with minimal hysteresis. Later we achieved an excellent power conversion efficiency PCE of 10.4% using a novel interface diffusion strategy where we modify the buried interface by PEAI. Remarkably, the devices retain 90% of their initial efficiency after 3500 hours of storage, demonstrating excellent long-term stability. The improved device performance is attributed to enhanced crystallisation dynamics, reduced lattice microstrain, improved microstructure, and suppressed charge carrier recombination. In addition, additives play a significant role in enhancing the morphology and crystallinity of the perovskite, consequently, improve the device performance. Using 2-Pyridal thiourea (2PTU) within the precursor solution to improve the structural and optoelectronic characteristics of the FAMASnI2.8Br0.2 film. As a result, the DMSO-free Sn-PSCs fabricated device showed a remarkable PCE of 11%. The device without any reducing agent demonstrated brilliant operational stability under maximum power point tracking (MPPT) conditions for 60 min. In summary, this research presents methodologies for designing and investigating DMSO-free Sn-PSCs. The research outcomes offer valuable directions for developing efficient and stable Sn-PSCs via a DMSO-free processing route.

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