Interfaces and electrodes engineering for perovskite solar cells: from rigid substrates to flexible applications

Abstract

Perovskite solar cells (PSCs) have emerged as a promising next-generation photovoltaic technology. However, their widespread commercialization is hindered by challenges at multiple device levels: significant non-radiative recombination losses at buried interfaces, inefficient and unstable charge extraction layers that limit scalability, and the absence of high-performance transparent electrodes for flexible applications. This thesis systematically addresses these interconnected bottlenecks through a multi-faceted research strategy, encompassing molecular-level interface engineering, scalable charge transport layer design, and the innovative development of a high-performance flexible electrode. The work progresses from fundamental mechanistic studies on rigid substrates to the demonstration of flexible devices, establishing a comprehensive pathway toward efficient, stable, and manufacturable PSCs. The specific contents are divided into the following three parts:
1. Buried interface passivation. I targeted the issue of defects and suboptimal energy level alignment at the buried interface in inverted p-i-n PSCs. A novel molecular passivation strategy was designed using a tailored amidino-based derivative (PDAII₂) to modify the SAM substrate. This molecular intervention effectively passivated interfacial defects, suppressing non-radiative recombination, and simultaneously modulated the crystallization kinetics of the perovskite layer. The resulting high-quality perovskite film featured enlarged grains and optimized energy level alignment at the SAM/perovskite junction. These improvements led to a champion PCE of 25.53% for rigid inverted PSCs. The devices also demonstrated exceptional environmental stability, retaining 85% of their initial efficiency after 1000 hours under ambient conditions (25°C, 50% RH). The passivation mechanism is substrate independent and provides a foundation transferable to flexible platforms.
2. Scalable buffer layer engineering. To bridge the lab-to-fab gap, I addressed the limitations of conventional organic electron transport layers (e.g., BCP) in large-area modules, which often suffer from incomplete coverage and performance non-uniformity. A pinhole-free, highly conformal SnO2 buffer layer deposited via atomic layer deposition (ALD) was introduced as a robust replacement. The ALD-SnO2 layer provided exceptional uniformity and intimate interfacial contact, enhancing vertical charge extraction and minimizing recombination losses. This engineering yielded a PCE of 23.85% for small-area devices. Crucially, the superior film quality enabled seamless scaling to a large-area mini-module (30 cm × 30 cm) that achieved a stabilized PCE of 17.30%, representing a significant absolute efficiency gain over BCP-based control modules. The conformal ALD process is particularly advantageous for flexible substrates.
3. Flexible transparent electrode development. To overcome the performance-flexibility dilemma imposed by brittle ITO electrodes, a high-performance semitransparent electrode based on an optimized PEI/Ag/PEI-Zn tri-layer architecture was developed. This design used a PEI seed layer to facilitate the formation of a continuous, ultra-thin Ag film, capped with a PEI-Zn composite layer acting as both an optical coupling layer and an electron transport layer. This structure achieved a balance between electrical conductivity (sheet resistance ~8 Ω/□) and optical transparency (~82% in the visible spectrum). FPSCs incorporating this electrode achieved a PCE of 19.24% and demonstrated exemplary mechanical durability, retaining 73% of their initial PCE after 500 bending cycles at a 5 mm radius.
In summary, this thesis presents a holistic optimization framework for perovskite photovoltaics, progressing from fundamental mechanistic studies on rigid substrates to the demonstration of flexible devices. The strategies address the core challenges of efficiency, stability, and manufacturability, providing valuable insights and practical solutions toward commercially viable perovskite solar cells.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Hainam Do (Supervisor) & Juan Wang (Supervisor)