A research group in China has fabricated a perovskite solar cell using a new molecular design approach aimed at reducing defects in the perovskite film and increasing device efficiency and stability.
“Rapid film crystallization can generate subtle defects that become concentrated at surfaces, grain boundaries, and buried interfaces,” the research’s lead author, Cong Chen, told pv magazine. “Although molecular additives can effectively mitigate these imperfections, their design requires a careful balance: strong interactions favor defect passivation, but excessive molecular packing or the formation of insulating interfacial layers can hinder charge transport.”
“Additive engineering offers a practical strategy to address these challenges by regulating crystallization while simultaneously passivating electronic defects,” he went on to say. “However, effective additives must balance strong defect binding with unhindered charge transport while ideally providing additional protection against environmental stress.”
The proposed molecular design approach is described as a steric-gated dual-site chelation (SGDC) strategy. It consists of a rigid three-dimensional adamantane scaffold bearing two carboxymethyl coordination arms that enable strong chelation of undercoordinated lead ions (Pb²⁺), while sterically regulating local molecular packing.
The scientists used an adamantane-based molecular additive known as ADA-DA, which was designed to passivate defects in perovskite films. Its two carboxymethyl groups can simultaneously coordinate with undercoordinated Pb²⁺, while its rigid three-dimensional adamantane core controls molecular packing and prevents excessive interfacial crowding.
“This combination enables steric-gated dual-site chelation, providing strong defect passivation without hindering charge transport,” Chen said. “Experimental measurements confirmed strong interactions of ADA-DA with both lead and iodide ions.”
The perovskite film resulting from the molecular strategy exhibited larger grains, fewer grain boundaries, and a more compact and smoother morphology, according to the research team. ADA-DA was distributed throughout the perovskite but preferentially accumulated near surfaces and grain boundaries, where defect passivation is most needed. Electrical measurements further confirmed a substantial reduction in both electron and hole trap densities.
The proposed perovskite solar cell was based on an inverted positive-intrinsic-negative (p-i-n) architecture consisting of an indium tin oxide (ITO) substrate, a hole transport layer (HTL) made of nickel oxide (NiOₓ) and a self-assembled monolayer, the perovskite film, a buckminsterfullerene (C60) electron transport layer (ETL), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact. The perovskite layer incorporating ADA-DA was deposited using a vacuum-flash crystallization process.
Under standard illumination conditions, the device achieved a power conversion efficiency of 27.39%, compared with 26.24% for a reference cell built without the proposed molecular strategy. The result was verified by an undisclosed independent third-party certification body, the researchers said.
In a further step, the academics scaled up the ADA-DA-modified device from small-area cells to bifacial mini-modules using either transparent ITO or indium zinc oxide (IZO) electrodes on both sides. Under glass/ITO-side illumination, a 13-cell module with an area of 163.93 cm² reached a peak power conversion efficiency of 22.21%, while under IZO-side illumination, a 12-cell module with an area of 151.32 cm² achieved an efficiency of up to 22.33%.
“The bifacial architecture combines high efficiency with transparency and illumination from either side, making it attractive for building-integrated photovoltaics (BIPV),” Chen stated. “More importantly, the 151.32 cm² ADA-DA module maintained nearly constant power output for over 5,000 h under continuous white light-emitting diode (LED) illumination. Its output decreased only from 1,028.5 to 1,024.1 mW, corresponding to 99.6% retention, demonstrating exceptional long-term operational stability.”
Both the cells and modules were described in “Steric-gated dual-site chelation enables 27.3% efficient perovskite solar cells and ultra-stable 22% bifacial modules”, published in Joule. The research team included scientists from Hebei University of Technology, Jiaxing Nanhu University, and Tianjin University.
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