Perovskite solar cell based on ‘multifunctional’ hole transporting material achieves 26.41% efficiency

Researchers at China's Tsinghua University developed a perovskite solar cell with a new hole transport material that promises enhanced efficiency and stability while also ensuring a scalable fabrication technique.

“The development of the new organic hole-transporting material, named T2, represents a significant breakthrough in perovskite solar cells, as it offers a performance advantage over conventional materials like spiro-OMeTAD,” the research's corresponding author, Chenyi Yi, told pv magazine. “The novel characteristics of T2, including its unique electronic, structural, and chemical properties, synergistically enhance the efficiency of hole extraction and significantly reduce charge recombination at the interface with the perovskite layer.”

In the paper “Highly efficient and stable perovskite solar cells via a multifunctional hole transporting material,” which was recently published in Joule, Yi and his colleagues explained that they built the cell with thermally evaporated perovskite films.

“Notably, the fabrication process that yields these thermally evaporated perovskite films is amenable to large-scale production, marking a departure from the spin-coating methods traditionally used,” he added.

The scientists synthesized the T2 using thiomethyl-substituted fluorene as the arm structure and spiro-[fluorene-9,9′-xanthene] (FX) as the core. According to them, this combination offers a better band alignment and hole extraction than the more expensive spiro-OMeTAD.

They fabricated the cell with a substrate made of fluorine-doped tin oxide (FTO), an electron transport layer (ETL) based tin oxide (SnO2), a perovskite absorber, a hole transport layer (HTL) based on T2, and a gold (Au) metal contact.

Tested under standard illumination conditions, the device achieved a power conversion efficiency of 26.41%, an open-circuit voltage of 1.175 V, a short-circuit current density of 26.47 mA cm⁻², and a fill factor of 84.94%. For comparison, a reference cell with an HTL based on spiro-OMeTAD reached an efficiency of 24.43%, an open-circuit voltage of 1.154 V, a short-circuit density of 25.94 mA cm⁻², and a fill factor of 81.57%.

The group claimed the result represents the highest efficiency ever recorded for a perovskite solar cell using “alternative” HTLs. “The cell based on T2 showed better stability under continuous illumination, thermal heating, and storage in ambient air compared with the cells with spiro-OMeTAD because of the suppressed ion migration and the resulting chemical reactions,” it also explained.

The researchers also said they were able to identify the atomistic origin of the improved hole extraction, which they attributed to a better energy level alignment and the overlapping partial local density of electronic states (LDOS) between the valence band maximum of perovskite absorber at the interface and T2 energy level.

Using this cell architecture, the academics also built a mini solar module with a substrate size of 5 × 5 cm², which was reportedly able to achieve an efficiency of 21.45%, an open-circuit voltage of 4.385 V, a short-circuit current density of 6.41 mA cm⁻², and a fill factor of 76.31%.

“This shift towards scalable fabrication techniques, coupled with T2's superior performance features, positions our cell as a transformative candidate for future photovoltaic technologies,” Yi concluded. “The advent of T2 paves the way for cost-effective, high-efficiency energy solutions with the potential for broad deployment.”

The research group also included scientists from the University of Ferrara in Italy and the Zurich University of Applied Sciences in Switzerland.