Advanced Interface and Crystallization Engineering Strategies for High Efficiency and Stable Perovskite Solar Cells

Organic-inorganic hybrid metal halide perovskite solar cells (PSCs) have rose as leading materials for next generation photovoltaics and transistors, owing to their high light absorption, cost-effective solution processability and tuneable bandgap. Despite significant progress in power conversion efficiency, which has exceeded 27%, stability remains a key challenge and poses a risk to commercialization. To address this issue, interface additive engineering and crystal control have become central areas of focus in both academia and industry. This dissertation explores strategies to enhance the efficiency and stability of PSCs through three primary methods. The main research content includes the following three parts: (1) Construction of Co-SAM and optimization of the top interface A dual-interface engineering approach was developed by integrating a Co-assembled monolayer (Co-SAM) at the p-type buried interface and a vacuum-quenched two-dimensional (2D) perovskite capping layer at the n-type top interface. The optimized Co-SAM improves the hole-transport-layer (HTL) and reduces leakage current, while vacuum-assisted fragmentation of the 2D layer achieved through phenethylammonium iodide (PEAI) annealing—ensures superior damp-heat stability. This strategy yielded an impressive open-circuit voltage (Voc) of 1.216 V (92% of the Shockley–Queisser limit) and a power conversion efficiency (PCE) of 23.68%. Notably, the champion devices exhibited excellent operational stability after maximum power point (MPP) tracking. (2) Modulating Intermediate Phase Formation to Enhance Photovoltaic Performance of Inverted FA-Based Perovskite Solar Cells Building upon the Co-SAM-modified contact framework, we shifted our focus to Formamidinium (FA)-based perovskites, which possess ideal optoelectronic properties and bandgaps but suffer from phase instability arising from uncontrolled nucleation of intermediate phases. To address this, we introduced poly(acrylonitrile-methacrylate) (PAM) as a crystallization modulator. PAM forms an intermediate complex with Lead (II) iodide (PbI₂), guiding controlled nucleation and oriented crystal growth, thereby stabilizing the α-phase. This method yielded a highly uniform and crystalline perovskite film. The resulting PAM-modified p-i-n device achieved a PCE of 25.30% and a Voc of 1.211 V, corresponding to 95% of the detailed-balance limit. The device also exhibited excellent thermal stability, retaining ≥90% of its original efficiency after 1000 hours of continuous 1 sun illumination at 65 °C. (3) Ligand Engineering for Stability Enhancement To further enhance operational stability, we employed a methylammonium-free (MA-free) perovskite and introduced triphenylphosphine oxide (TPPO) at the perovskite/electron transport layer (ETL) interface. TPPO effectively passivates under-coordinated Pb²⁺ sites, reducing surface defects and suppressing ion migration. The TPPO-modified device achieved a champion PCE of 26.01% and a Voc of 1.230 V, corresponding to the lowest voltage deficit (0.320 V) reported for MA-free PSCs. Furthermore, TPPO suppressed halide and silver ion migration, significantly enhancing device longevity. Under continuous MPP tracking, the devices maintained 90% of their initial efficiency after 1200 hours of operation, marking a breakthrough in long-term device reliability. This work presents a comprehensive strategy for advancing perovskite solar cells by synergistically optimizing interface engineering, crystallization dynamics, and molecular passivation. The integration of Co-SAMs and 2D capping layers enhances charge extraction and damp-heat stability; PAM-mediated crystallization delivers uniform, stable FA-based films; and TPPO mediated passivation minimizes interfacial defects and ionic instability. Together, these advances raise device efficiency beyond 26% while ensuring robust operational stability, providing a promising pathway toward the commercial deployment of perovskite photovoltaics.