A group of researchers from China’s Soochow University and Chinese PV manufacturer Longi has developed a perovksite-silicon tandem solar cell through an interfacial strategy that reportedly suppresses non-radiative recombination while preserving efficient charge extraction.
The proposed strategy consists of integrating a discrete monoclinic zirconia (ZrO2) nanoparticle between the cell’s transparent conductive oxide (TCO) and the self-assembled monolayer (SAM) layer. “This modulates the local surface energy to facilitate the growth of void-free, large-grain perovskite films, while simultaneously serving as a nanoscale localized contact,” Longi researcher He Bo told pv magazine. “In contrast to conventional metal oxide dielectrics, ZrO₂ exhibits a high dielectric constant, which mitigates interfacial charge accumulation and suppresses hysteresis.”
The scientists explained that the ZrO₂ interfacial layer acts as a discontinuous, nanoporous buffer between the transparent conductive oxide and the SAM, effectively passivating the buried interface without hindering charge transport. Owing to its wide bandgap of around 5.49 eV, ZrO₂ introduces negligible visible-light absorption, while its porous structure reduces direct contact between the perovskite and defective conductive oxide, thereby suppressing leakage pathways and interfacial recombination.
Meanwhile, the exposed SAM regions maintain efficient hole extraction, with structural characterization confirming the formation of phase-pure monoclinic ZrO₂. Scanning electron m icroscope (SEM) analysis also showed that precursor dilution controls nanoparticle coverage providing effective interfacial passivation while avoiding the formation of a continuous insulating layer that could impede carrier extraction.
The researchers built the monolithic perovskite-silicon tandem solar cell with a crystalline silicon (c-Si) bottom cell and an inverted p-i-n perovskite top cell.
The silicon subcell features intrinsic amorphous silicon (a-Si(i)) and doped nanocrystalline silicon oxide (nc-SiOₓ(n)) passivating contacts, with indium tin oxide (ITO) and silver (Ag) forming the rear contact. On the front side of the silicon cell, the nc-SiOₓ(n)/a-Si(i) contact stack is combined with ITO to form the recombination/contact region connecting the two subcells.
The ZrO₂ interfacial layer was introduced between the ITO and the MeO-4PACz self-assembled monolayer (SAM), followed by the perovskite absorber. The top cell was then completed with a lithium fluoride/ethylenediammonium diiodide (LiF/EDAI) interfacial passivation layer, a fullerene (C₆₀) electron-transport layer, a tin oxide (SnO₂) buffer layer, and an indium zinc oxide (IZO) transparent conductive electrode. Finally, a magnesium fluoride (MgF₂) anti-reflection coating and Ag fingers form the front optical and electrical contacts.
The optimized ZrO₂ interlayer was found to improve the integrity and molecular organization of the self-assembled monolayer (SAM), with conductive atomic force microscopy (C-AFM) showing fewer localized high-conductivity regions, indicating more homogeneous SAM coverage and reduced leakage pathways.
Moreover, X-ray photoelectron spectroscopy (XPS) confirmed the formation of covalent Zr–O–P bonds creating a dual-anchoring network that strengthens SAM attachment to the interface. Ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe force microscopy (KPFM) revealed a favorable energy-level alignment and hole extraction.
Tested under standard illumination conditions, the tandem cell achieved a power conversion efficiency of 34.0%, an open-circuit voltage of 1.997 V, short-circuit current density of 20.36 mA cm⁻², and fill factor of 83.62%. The researchers also reported an independently certified open-circuit voltage of 2.014 V.
The device was also found to retain 84% of its initial efficiency after 2000 h, while a control cell built without the proposed interfacial strategy degraded to 70% after 1000 h.
“These results highlight an effective interfacial engineering strategy for simultaneously delivering high efficiency, enhanced voltage, and long-term operational stability,” Bo stated.
The new cell concept was presented in the paper “Nanoscale interfacial scaffold enables perovskite/silicon tandems with 34% efficiency and an open-circuit voltage over 2.01 V,” published in Science Bulletin.
Longi currently holds the world record for perovskite-silicon tandem solar cell efficiency, with a 35.5%-efficient two-terminal device. The result was independently certified in July by the European Solar Test Installation (ESTI), part of the European Commission’s Joint Research Centre in Italy.
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