Perovksite-TOPCon tandem solar cell based on self-assembled monolayer achieves 31.1% efficiency

Researchers in China have fabricated a perovskite-TOPCon solar cell with a top perovskite device utilising a self-assembled monolayer aimed to improved cell stability. The tandem cell achieved a high fill factor and a certified efficiency of 30.9%.

June 6, 2025 Emiliano Bellini

An inverted perovskite solar cell built by researchers at the Zhejiang University

Image: Zhejiang University

A group of researchers led by the Zhejiang University in China has fabricated a perovskite-TOPCon tandem solar cell with a top inverted perovskite cell utilising a self-assembled monolayer (SAM) that can reportedly enhance the cell’s thermal stability.

Inverted perovskite cells have a device structure known as “p-i-n”, in which hole-selective contact p is at the bottom of intrinsic perovskite layer i with electron transport layer n at the top. Conventional halide perovskite cells have the same structure but reversed – a “n-i-p” layout. In n-i-p architecture, the solar cell is illuminated through the electron-transport layer (ETL) side; in the p-i-n structure, it is illuminated through the hole‐transport layer (HTL) surface.

The scientists explained that electron density within the SAMs can be modulated to shift the interfacial energetics between the SAM and perovskite layer, which results in a “more versatile and controlled approach” to optimising energy alignment in the perovskite solar cell, while also having a “negligible” influence on the phase stability of the wide-bandgap perovskite film.

The team built the top perovskite cell with an indium tin oxide (ITO) layer, the SAM, a nickel oxide (NiO) layer, a perovskite absorber with an energy bandgap of 1.68 eV, a lithium fluoride (Lif) layer, an electron transport layer (ETL) based on buckminsterfullerene (C60) and tin oxide (SnO₂), a transparent back contact made of indium zinc oxide (IZO), and a silver (Ag) metal contact.

Cross-sectional SEM image of a perovskite/silicon tandem solar cell without the deposition of LiF and AgImage: Zhejiang University, nature communications, CC BY-NC-ND 4.0

Tested under standard illumination conditions, the top perovskite cell was found to have a power conversion efficiency of 22.8%, an open-circuit voltage of 1.24 V, and a “high” fill factor of 84.3%. It was also found to retain more than 99% of the initial efficiency after 400 h of maximum power point tracking at 60 C.

Using this cell, the researchers built a 1 cm²tandem device including a standard TOPCon solar cell as a bottom device.

This cell achieved an internally measured efficiency of 31.1% and a certified efficiency of 30.9%, with the Chengdu Institute of Product Quality Inspection Co., Ltd. National Photovoltaic Product Quality Inspection & Testing Center having verified the result.

It also achieved an open-circuit voltage of 1.88 V, and a short-circuit current of 20.0 mA cm⁻², and a “high” fill factor of 82.6%.

The researchers claimed these figures demonstrate the reliability and potential application of the inductive effect modification strategy for wide-bandgap perovskite solar cells.

“The results highlight the possibility of the rational design of SAMs by making use of the inductive effect to achieve favored interfacial energetics with wide-bandgap perovskite,” they emphasised. “We believe this strategy is promising in contributing to the commercialisation of perovskite and perovskite-TOPCon tandem solar cells.”

The novel cell concept was presented in the paper “Inductive effects in molecular contacts enable wide-bandgap perovskite cells for efficient perovskite/TOPCon tandems,” which was recently published in nature communications.

In July, other researchers from the Zhejiang University in China announced to have developed for the first time an inverted perovskite solar cell based on a high-entropy hybrid perovskite material that reportedly improves the device’s stability while providing excellent efficiency levels.

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