Researchers at the University of Rome Tor Vergata in Italy have developed 15 cm x 15 cm inverted perovskite solar modules based on a hole transport layer (HTL) made of inorganic nickel oxide (NiOx).
“Our research stands out for optimizing the deposition of nickel oxide over a large area using the blade coater, a scalable technique that is fundamental to reducing the technological gap between basic research and commercialization,” the research's lead author, Luigi Angelo Castriotta, told pv magazine. “This technique has been optimized to be performed in standard ambient conditions with 25% average humidity, eliminating the need for controlled environments such as nitrogen, which are often used in traditional manufacturing methods.”
In inverted perovskite solar cells and modules, the perovskite cell material is deposited onto the HTL and then coated with an electron transport layer (ETL) – the opposite way round to conventional device architecture. Inverted perovskite solar devices typically show strong stability, but have lagged behind conventional devices in terms of conversion efficiency and cell performance.
The scientists explained that inverted perovskite cells commonly utilize an HTL based on poly(triarylamine) (PTAA), which they said is known for its high performance in printable devices. Their choice for NiOx was due to the enhanced long-term stability this material offers, on top of similar efficiency levels compared to PTAA. “In contrast to PTAA, NiOx is potentially low-cost due to its inorganic nature, is highly photostable, chemically stable, has excellent optical transmittance, and has a hydrophilic nature,” they explained.
They also warned, however, that integrating the NiOx HTL under ambient conditions using printable methods results in lower efficiencies compared to PTAA-based devices. To solve this issue, they decided to print NiOx over the cell, without any spin coating step, via so-called doctor blading, a method generally used to form films with well-defined thicknesses.
“We did the doctor blading of nickel(II) chloride (NiCl2·6H2O) solution on indium tin oxide (ITO) substrates ambient conditions,” the group explained. “Then, the films were annealed at 300 C to promote decomposition and oxidation, leveraging atmospheric oxygen to form the NiOx film.”
The solar panel was built with an ITO substrate, the NiOx HTL, a self-assembled monolayer (SAM) made of [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz), a perovskite absorber, an ETL relying on buckminsterfullerene (C60), a bathocuproine (BCP) buffer layer, and a copper (Cu) metal contact.
Image: Image: University of Rome Tor Vergata, communications materials, Common License CC BY 4.0
The first four layers were fabricated via doctor blading in ambient conditions, while the remaining ones were assembled via thermal evaporation.
“We found that introducing the SAM between nickel oxide and perovskite significantly improves the morphology and uniformity of the perovskite film, reducing defects such as pinholes and increasing the stability of the device over time,” Castriotta explained. “
Tested under standard illumination conditions, the 110 cm² perovskite panel achieved a power conversion efficiency of 12.6%, a short-circuit current density of 19.67 mA/cm2, and a fill factor of 63.49%. The device was also able to retain 84% of its initial efficiency after 1000 h of thermal stress testing at 85 C in air.
“These results underscore the potential of NiOx in PSCs and open new avenues for the large-scale, cost-effective production of perovskite solar modules,” the academics stated. “Future research should focus on further optimizing the fabrication process and exploring the commercial viability of these technologies.”
The novel approach was presented in the study “Stable and sustainable perovskite solar modules by optimizing blade coating nickel oxide deposition over 15 cm × 15 cm area,” published in communications materials.
“Our research not only addresses one of the main obstacles to the commercialization of perovskite solar cells, namely the scalability of the manufacturing process, but does so with a sustainable approach that avoids the use of toxic solvents and complex manufacturing environments,” Castriotta stated. “The result is a promising technology that can accelerate the adoption of perovskite solar cells at industrial scale, while maintaining high efficiency and long-term stability.”
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