Researchers from Bar-Ilan University, Israel; the Institute of Astronomy Space and Earth Science, India; Prabhat Kumar College, India; the University of Waterloo, Canada; the University of Goettingen, Germany; Sidho-Kanho-Birsha University, India; and the Indian Institute of Science, India have developed mini perovskite solar modules that combine competitive efficiency with over 1,300 hours of operational stability by engineering the buried hole-transport interface with reduced graphene oxide (r-GO).
The work targets one of the main bottlenecks in perovskite photovoltaics - scaling from high-efficiency small cells to stable, larger-area modules - by systematically passivating the interface between a self-assembled monolayer (SAM)-based hole transport layer (HTL) and the perovskite absorber.
In their p-i-n perovskite solar mini-modules (PSMs), the team introduces a thin r-GO layer directly on top of the SAM HTL to simultaneously passivate interfacial defects and modulate perovskite crystallization. SAM-based HTLs are attractive due to their chemical inertness, moisture resistance, optical transparency, and UV stability, along with favorable energy-level alignment with the perovskite valence band that suppresses interfacial recombination and supports long-term stability. However, SAM layers can suffer from low hole mobility, surface defects, and poor wetting of the perovskite precursor solution, which limit charge extraction and film coverage. The r-GO interlayer addresses these issues by providing a lower-energy, better-wetting surface for the perovskite precursor, slowing crystallization and promoting larger, higher-quality perovskite grains with fewer grain boundaries. Literature also indicates that r-GO can participate in reduction reactions with metal halide perovskites and act as a barrier layer between HTL and perovskite, helping to maintain perovskite phase stability rather than accelerating photodegradation.
To implement this interface design, the researchers spin coat r-GO onto the SAM-modified substrate before depositing the perovskite via a two-step spin-coating process with anti-solvent treatment. The device stack used for the cell architecture comprises a glass/ITO substrate, a sputtered nickel oxide (NiOx) layer serving as the seed for the SAM, the SAM itself, the r-GO interfacial layer, a perovskite absorber, a C60-based electron transport layer (ETL), an aluminum-doped zinc oxide (AZO) transparent back contact, a bathocuproine (BCP) buffer layer, and a copper (Cu) metal contact. Using this structure, the team first realizes a single cell with a power conversion efficiency (PCE) of 22.59%, which is then upscaled to mini-modules through monolithic interconnection. The monolithic 5 cm × 5 cm modules are fabricated via a P1-P2-P3 laser scribing sequence: P1 defines isolation lines in the ITO, followed by deposition of NiOx, SAM, and r-GO; the perovskite layer is then formed with the two-step spin coating and thermal annealing; P2 selectively removes layers to form interconnects between subcells after Cu deposition; and P3 isolates the top electrodes to avoid electrical cross-talk and complete the module layout.
Performance was evaluated on unencapsulated mini-modules with an active area of 9.2 cm² under standard AM1.5G (1-sun) illumination using J-V measurements with a calibrated solar simulator and source meter. Control modules without r-GO achieved a PCE of 15.13%, while r-GO-treated modules reached 16.6 - 16.66%, demonstrating a clear performance gain from the interfacial engineering. Under maximum power point tracking (MPPT) and continuous illumination, the r-GO-treated, unencapsulated mini-modules retained approximately 95% of their initial PCE after 1,300 hours of operation, significantly outperforming control devices. In ambient conditions, r-GO-treated modules retained about 90% of their initial efficiency, whereas control modules dropped to roughly 60%, underscoring the stabilizing effect of the r-GO/SAM interface on perovskite modules. Electrical characterization revealed that r-GO-modified substrates yield perovskite films with fewer defects, improved growth kinetics, reduced grain boundaries and trap densities, higher recombination resistance, and enhanced carrier dynamics, all of which contribute to improved charge transport and suppressed nonradiative losses.
The interface-passivation concept is notable in that r-GO has previously been explored mainly in small-area perovskite solar cells, while here it is fully integrated into a monolithic mini-module process that is compatible with scalable fabrication. By combining SAM-based HTLs for robust, transparent, and energetically well-aligned hole extraction with r-GO to address mobility, defect, and wetting limitations, the researchers demonstrate a practical route to bridge the gap between lab-scale devices and more commercially relevant module formats. As the authors put it, “These results demonstrate that r-GO interfacial passivation combined with optimized transport layers is an effective route toward more efficient and durable perovskite modules.”
