World record: China’s flexible perovskite-silicon tandem solar cell hits 33.35% efficiency
A Chinese company’s flexible perovskite-silicon tandem solar cell has achieved a power conversion efficiency of 33.35%. Longi’s solar cells’ performance result was certified by the United States’ National Renewable Energy Laboratory (NREL).
This marks the first and only world record efficiency for a flexible crystalline silicon-perovskite tandem solar cell certified by an international authoritative body in the global photovoltaic field, according to Longi.
This breakthrough lays a solid foundation for the commercial development of flexible silicon-based tandem cells in lightweight/flexible high-power photovoltaic applications such as space photovoltaics and vehicle-integrated photovoltaics, according to Longi.
Next-generation photovoltaic technology
The company’s cells’ high efficiency comes at a time when perovskite tandem solar cells have emerged as promising candidates for next-generation photovoltaic technology due to their ultra-high power conversion efficiency.
A dual-buffer-layer strategy with a stress-release mechanism was implemented to synergistically mitigate ion bombardment during subsequent sputtering deposition and enhance interfacial adhesion while preserving efficient charge extraction.
The flexible tandem solar cell, based on this dual-buffer-layer, constructed on a 60-micron-thick ultra-thin silicon bottom cell, achieves a certified PCE of 33.4% on a 1-cm2 area, and a certified PCE of 29.8% on a wafer-sized area of 260-cm2 with a power-per-weight of up to 1.77 W/g.
Modified tandem solar cells demonstrate good durability
The modified tandem solar cells demonstrate good durability, retaining over 97% of their initial power conversion efficiencies after 43000 bending cycles under a maximum curvature radius of around 40 mm in air, and around 97% after thermal cycling testing (−40 °C to 85 °C) for 250 cycles, according to the work published in Nature.
The resulting top cell features a SnOx bilayer contact structure, the C60 layer, a transparent back contact made of indium zinc oxide (IZO), a silver (Ag) metal contact, a perovskite absorber, a lithium fluoride (LiF) layer, and a self-assembled monolayer hole transport layer composed of ethylenediammonium diiodide (EDAI). Longi did not disclose whether the bottom silicon cell uses a heterojunction (HJT) or TOPCon design, as reported by PV Magazine.
Dual-buffer layer strategy improves interfacial adhesion
Longi has maintained that the dual-buffer layer strategy improves interfacial adhesion while maintaining efficient charge extraction. The company claims that the interfacial adhesion is particularly critical in flexible tandem devices, which endure greater mechanical stress from bending compared to rigid cells.
Longi team applied a first tin oxide (SnOx) buffer layer to protect the perovskite and transport layers during the transparent conducting oxide sputtering process, performed via atomic layer deposition (ALD).
A second SnOx layer was then deposited through chemical vapor deposition (CVD) to enhance charge extraction and reduce resistive losses at the interface with the buckminsterfullerene (C60) layer, which is prone to delamination under environmental stress.
This double-layer structure design precisely resolves the conflict between the needs for stress buffering and efficient transport at the micro-nano scale. It ensures the tandem device achieves excellent bending durability while maintaining compatible and outstanding power generation capability.