CAS researchers report 22.7% efficiency in methylammonium-free perovskite module

Researchers at the Chinese Academy of Sciences (CAS) and Dalian Jiaotong University have developed a methylammonium-free perovskite solar module with an area of 54.80 cm².

The work focuses on eliminating methylammonium, a component known to cause instability in these devices. By removing this element, the researchers aimed to create a more durable and reliable solar cell structure.

The findings were published in the journal Advanced Materials, detailing the specific chemical and processing methods used to achieve these results.

Performance and Stability

• Small-area cells achieved an efficiency of 26.16%.
• The 54.80 cm² module reached 22.70% efficiency, significantly higher than the 15.8% recorded for the reference module.
• The methylammonium-free device retained 97.76% of its initial efficiency after 1,300 hours of testing.
• In comparison, the reference device retained only 65.86% of its original efficiency after the same duration.
• Both devices underwent testing under continuous operation at the maximum power point, AM 1.5G illumination, and a temperature of 65°C.

Chemical Mechanism

The instability of methylammonium (MA) in perovskite devices stems from its tendency to decompose under thermal and chemical stress. This breakdown releases methylamine and hydrogen iodide, which promotes the formation of lead iodide, a process that degrades the cell structure. To address this, the CAS and Dalian Jiaotong University team incorporated rubidium thiocyanate (RbSCN) and formamidinium thiocyanate (FASCN) as additives.

Manufacturing Process

Zhihua Zhang, the corresponding author affiliated with the Chinese Academy of Sciences (CAS) and Dalian Jiaotong University, described how the team established a dependable method for producing uniform, high-efficiency, methylammonium-free perovskite solar modules. By utilizing slot-die coating in ambient settings, this technique eliminates the necessity for the strict environmental controls typically demanded by conventional manufacturing methods.

Zhang emphasized that instead of enforcing stricter limits on process regulation, the research enhances the crystallization process’s resilience to processing fluctuations. The combined application of RbSCN and FASCN as additives reduces the energy barrier required for the δ-to-α phase transition. This chemical modification significantly expands the processing window between film deposition and annealing to exceed 100 seconds, thereby providing increased flexibility during production.

Phase Transition Dynamics and Film Quality

RbSCN and FASCN additives function via an in situ coordination mechanism that drives the transformation of the non-photoactive δ-phase into the photoactive α-phase while inhibiting the emergence of undesired secondary phases. By lowering the energy barrier separating these two phases, the process encourages the development of the specific crystal structure required for optimal light absorption and charge transport. The resulting expanded processing window supports the creation of dense films featuring large crystal grains, a consistent vertical compositional gradient, and reduced residual stress. Corresponding author Zhihua Zhang observed that the combined application of these additives "substantially broadens the processing window between film deposition and annealing." This methodology enables the regulated deposition of perovskite precursor inks across extensive substrates, yielding uniform thin films with significantly less material waste than traditional spin coating techniques.