A group of researchers from the Chinese Academy of Sciences (CAS) and Dalian Jiaotong University have fabricated a small-sized solar module based on a perovskite material that doesn’t contain methylammonium (MA) molecules. These molecules have intrinsic thermal instability and contribute to increasing the typical thermal instability of perovskite PV devices.
MA negatively affects the stability of perovskite solar cells primarily because of its intrinsic thermal and chemical instability. At elevated temperatures, MA-containing perovskites such as MAPbI₃ can undergo decomposition, releasing volatile species such as methylamine (CH₃NH₂) and hydrogen iodide (HI). This promotes the degradation of the perovskite crystal structure and the formation of lead iodide (PbI₂), leading to increased defect density, reduced charge-carrier performance, and ultimately lower photovoltaic efficiency.
“We developed a reliable fabrication process for uniform, high-efficiency, methylammonium-free perovskite solar modules using slot-die coating under ambient conditions,” corresponding author Zhihua Zhang told pv magazine. “Slot-die coating is a highly attractive technique for the large-scale manufacturing of perovskite solar cells, combining efficient material utilization with seamless integration into continuous roll-to-roll production processes.”
Unlike conventional spin coating, slot-die coating enables controlled deposition of perovskite precursor inks over large substrates, facilitating the formation of uniform thin films with minimal material waste. However, achieving homogeneous film coverage and controlled crystallization remains challenging, particularly when transitioning from laboratory-scale devices to large-area modules.
Against this backdrop, the researchers used a combined additive (CA) strategy based on rubidium thiocyanate (RbSCN) and formamidinium thiocyanate (FASCN) to control how perovskite crystals form and evolve during deposition. This approach widens the processing window for slot-die coating under ambient conditions, making it easier to produce high-quality films. The two additives work together through an in situ coordination mechanism that facilitates the conversion of the non-photoactive δ-phase into the photoactive α-phase while preventing the formation of unwanted secondary phases.
The photoactive α-phase is crucial for solar cell performance, as it enables efficient light absorption and charge transport, whereas the δ-phase contributes little to electricity generation. By reducing the energy barrier between these two phases, the additives promote the formation of the desired crystal structure and limit the presence of non-photoactive material. This improved control over crystallization helps produce more uniform perovskite films with fewer undesired phases.
“Rather than imposing tighter constraints on process control, this work makes the crystallization process itself more tolerant of processing variability,” said Zhang. “The synergistic use of RbSCN and FASCN as combined additives lowers the energy barrier for the δ-to-α phase transition and substantially broadens the processing window between film deposition and annealing.”
The combined effect of the two additives extended the processing window for uniform perovskite crystallization to more than 100 seconds. This enabled the formation of dense, high-quality films characterized by large crystal grains, a uniform vertical compositional gradient, and lower residual stress.
The researchers achieved a power conversion efficiency of 26.16% in small-area solar cells, while a larger module with an active area of 54.80 cm² reached 22.70%. This represented a significant improvement over the 15.8% efficiency recorded for a reference module fabricated without the additive strategy, the scientists said.
The approach also delivered substantial gains in operational stability. Unencapsulated devices maintained 97.76% of their initial efficiency after 1,300 hours of continuous operation at the maximum power point under AM 1.5G illumination and a temperature of 65 C. Under identical testing conditions, reference devices retained just 65.86% of their original efficiency.
The new cell concept was presented in “Processing Window Expansion Enables Uniform Crystallization in Scalable Ambient-Fabricated Perovskite Photovoltaics,” published in Advanced Materials.
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