Perovskite-silicon tandem solar cell built on textured silicon reaches 30.77% efficiency

A research team led by scientists at China’s Nanjing University has developed a healing intervention strategy to improve the efficiency and stability of perovskite-silicon tandem solar cells based on industrial textured silicon.

Textured silicon is particularly important for perovskite-silicon tandem cells because microscopic pyramids on the silicon surface reduce reflection and improve light trapping, increasing the amount of sunlight available for conversion. Such textures are widely used in industrial crystalline silicon solar cells, but their uneven surfaces make it difficult to deposit uniform, defect-free perovskite layers. Achieving conformal perovskite coverage on industrial textured silicon is therefore an important step toward combining high tandem efficiencies with established silicon cell manufacturing processes.

To address this challenge, the researchers applied methylammonium thiocyanate (MASCN) to the perovskite film after its formation. The treatment promoted further crystal growth while maintaining conformal coverage of the textured silicon surface.

“We employ a healing intervention strategy for perovskite top cells, in which an MASCN solution is applied to the as-prepared films to achieve conformal coverage on textured silicon,” the scientists explained. “This approach enables the formation of high-quality perovskite films with minimal grain boundaries, low defect densities, and exceptional stability on various substrates through an Ostwald ripening process.”

The research team used n-type silicon wafers textured on both sides and cut the 4-inch wafers into 2.5 cm × 2.5 cm substrates. The scientists deposited hydrogenated amorphous silicon and indium tin oxide (ITO) layers to form the silicon bottom cell and then thermally co-evaporated lead iodide and cesium bromide onto its textured front surface. They subsequently spin-coated formamidinium iodide and formamidinium bromide to form the perovskite top cell.

For the treated devices, the researchers applied MASCN to the newly formed perovskite film to promote further crystal growth. They then heated the devices at 90 C under nitrogen and annealed them at 150 C in air.

The scientists subsequently applied a passivation treatment and deposited a C60 electron transport layer, tin oxide, a transparent indium zinc oxide (IZO) electrode, silver contacts, and a magnesium fluoride antireflection coating.

The tandem cell was built with a silver (Ag) rear contact, an indium tin oxide (ITO) layer, the silicon bottom cell, another ITO layer, a nickel oxide (NiOx) hole transport layer, a self-assembled monolayer (SAM), and a wide-bandgap (WBG) perovskite absorber. The device also featured a fullerene (C60) electron transport layer, a tin oxide (SnO2) buffer layer, an indium zinc oxide (IZO) transparent electrode, silver contacts, and a magnesium fluoride (MgF2) antireflection coating.

The researchers used scanning electron microscopy to examine film coverage and grain structure, as well as X-ray measurements to assess crystallinity and crystal orientation. They also used photoluminescence and electrical measurements to investigate charge recombination and the film interfaces.

The team compared the electrical performance of treated and untreated control cells, measured the spectral response of each tandem subcell, obtained independent certification for its best-performing device, and tested an encapsulated cell under continuous illumination for 3,400 hours.

“The resulting 1.68 eV wide-bandgap perovskite solar cells achieve a champion efficiency of 21.1%, contributing to a certified stabilized tandem efficiency of 30.77% and an impressive open-circuit voltage of 1.915 V over an active area of 1.164 cm²,” the researchers said. “Notably, an encapsulated device retains its initial performance after 3,400 hours of continuous maximum power point tracking under one-sun illumination in ambient conditions, representing the excellent stability in perovskite/silicon tandem cells reported to date.”

The scientists presented their findings in “Healing intervention for improving the efficiency and stability of tandem devices on industrial textured silicon,” published in Nature Communications.

“This study presents an effective technique for enhancing the quality of perovskite films fabricated via a hybrid two-step deposition method, thereby addressing the photovoltage-loss-induced efficiency limitation in industrial silicon-based tandem solar cells,” the academics concluded.

Scientists from China’s Nanjing University, Renshine Solar (Suzhou), Zhejiang Provincial Innovation Center of Laser Intelligent Equipment Technology, Yunnan University, and Sweden’s Uppsala University contributed to the study.

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