The escalating global energy demand necessitates the development of renewable energy sources. Perovskite solar cells (PSCs) are highly promising due to their high power conversion efficiency (PCE), cost-effectiveness, versatility, and diverse applications. Laboratory-scale PSCs have achieved PCE exceeding 26%, signifying their potential to revolutionize the solar industry. However, significant hurdles impede their large-scale adoption, primarily concerning scalability, stability, and environmental impact. Conventional techniques like spin coating are inefficient for large-scale production, leading to substantial material waste and limited scalability. Furthermore, the need for sustainable, ambient-air fabrication processes is crucial for commercialization, as nitrogen environments commonly used in labs are not suitable for industrial settings. Alternative large-area deposition methods, including blade coating, slot-die coating, spray coating, screen printing, and inkjet printing, are being explored. Meniscus coating technologies, such as blade and slot coating, are particularly attractive due to their versatility, efficiency, and compatibility with roll-to-roll (R2R) manufacturing. Inverted PSC architectures (p-i-n) are preferred for their improved stability and reduced hysteresis, making them more suitable for commercialization. While poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) is a common hole transport layer (HTL), inorganic HTLs like nickel oxide (NiOx) offer advantages such as low cost, high photostability, chemical stability, excellent optical transmittance, and hydrophilic nature. This research focuses on optimizing blade coating of NiOx for large-area PSCs to address the challenges of scalability and sustainability.

Numerous studies have demonstrated the potential of NiOx as a high-performance HTL in small-scale PSCs, achieving PCEs up to 23.6%. However, a significant gap exists between small-scale and large-area printable NiOx-based PSCs, especially concerning ambient air deposition. For example, a shift from controlled environments to ambient air deposition resulted in a considerable decrease in PCE, from 20.7% for small-scale (0.1 cm²) devices to 10.34% for modules with a 3.7 cm² active area. Previous research has explored various deposition methods for NiOx, including printable techniques like meniscus and spray coating and non-printable methods such as evaporation and chemical bath deposition. Printable methods are preferred for their scalability and cost-effectiveness. While ambient air processing with printable methods is possible, it often results in lower PCE compared to cells fabricated under controlled conditions. This research aims to bridge this performance gap by optimizing blade coating of NiOx for large-area modules under ambient conditions.

This study investigated the feasibility of upscaling printable NiOx-based perovskite solar modules in ambient air. A procedure was developed to blade coat NiOx onto 15 cm × 15 cm substrates, eliminating the need for spin coating. Modules with a 110 cm² active area were fabricated using doctor blading for the NiOx/MeO-2-PACz/perovskite stack in ambient conditions, with thermal evaporation for the remaining layers. The NiOx ink concentration was optimized, and a self-assembled monolayer (SAM) was introduced to improve performance. The impact of varying NiCl2·6H2O precursor concentrations (0.15 M, 0.075 M, 0.050 M, and 0.037 M) on film thickness and uniformity was evaluated using ellipsometry. X-ray photoelectron spectroscopy (XPS) and X-ray reflectometry (XRR) were employed to characterize the oxidation states of NiOx and film uniformity. Perovskite layer deposition utilized a two-step blade coating process with a non-toxic solvent system. A SAM of MeO-2PACz was introduced at the HTL/perovskite interface to improve adhesion and film morphology. The completed module structure included evaporated C60/BCP as the electron transport layer (ETL), laser scribing for patterning, and a Cu electrode. Photovoltaic parameters were measured using a class A sun simulator, and long-term stability was assessed using the ISOS-T-1 thermal test at 85 °C in ambient air for 1000 hours.

The optimization of NiOx ink concentration showed a trade-off between film uniformity and thickness. The 0.05 M (1:2 dilution) concentration provided the best balance, resulting in improved film uniformity and a denser atomic packing. XPS analysis revealed a correlation between precursor concentration and NiOx oxidation states, with higher oxidation states observed at lower concentrations. XRR measurements confirmed that lower precursor concentrations resulted in increased electron density despite reduced film thickness. The introduction of the MeO-2PACz SAM at the HTL/perovskite interface significantly improved the perovskite film morphology, eliminating pinholes and enhancing uniformity. The champion module, with an active area of 110 cm², achieved a power conversion efficiency of 12.6%, with an open-circuit voltage (Voc) of 22.3 V, a short-circuit current (Isc) of 98.13 mA, and a fill factor (FF) of 63.49%. The module exhibited a near-unity hysteresis index of 1.02, indicating consistent performance in forward and reverse scans. Remarkably, the encapsulated module retained 84% of its initial efficiency after 1000 hours of thermal stress testing at 85 °C in ambient air, surpassing the stability of previously reported printable large-area perovskite solar modules fabricated in ambient conditions.

This research demonstrates the successful upscaling of printable NiOx-based perovskite solar modules in ambient air, addressing a critical challenge in the field. The optimized blade coating process, combined with the introduction of a SAM, significantly improved the performance and stability of the modules. The achievement of 12.6% PCE in a large-area (110 cm²) module under ambient conditions and its remarkable long-term stability represent a substantial advancement. The results highlight the potential of NiOx as a cost-effective and stable HTL for large-scale PSC production, reducing dependence on controlled environments and minimizing material waste. This environmentally friendly approach using non-toxic solvents contributes significantly to the sustainability of PSC technology.

This study demonstrates significant progress in the scalable fabrication of high-efficiency and stable perovskite solar modules. The optimized blade coating of NiOx, coupled with the use of a SAM and a non-toxic solvent system, enabled the creation of a 110 cm² module achieving 12.6% PCE and exhibiting exceptional long-term stability (84% efficiency retention after 1000 hours at 85 °C in air). This work bridges the performance gap between small-scale lab devices and large-area modules, paving the way for more cost-effective and environmentally sustainable perovskite solar technology. Future research should focus on further optimization of the blade coating process, exploring alternative SAMs, and investigating the long-term stability under various environmental conditions to ensure commercial viability.

While this study demonstrates impressive progress, some limitations exist. The observed thickness gradient in the perovskite film, attributed to the doctor blading process, might slightly affect the overall module performance. Further optimization of the blade coating parameters could potentially minimize this gradient and enhance uniformity. The long-term stability test was conducted under specific conditions (85 °C in air). Further testing under diverse environmental conditions (e.g., humidity, UV exposure) is necessary to fully assess the module's robustness and longevity. The research focused on a specific perovskite composition. Investigating the effectiveness of this blade coating method with other perovskite formulations would broaden its applicability.