A group of researchers led by China's Northwestern Polytechnical University has developed a two-terminal (2T) perovskite-silicon tandem solar cell through an interfacial engineering strategy that removes the residual lead(II)iodide (PbI2) from the wide-bandgap top perovskite cell without damaging its lattice.
PbI2 formation in wide bandgap perovskite solar cells arises from incomplete precursor conversion during crystallization and often leads to a reduction in device performance. Although small amounts of PbI₂ can provide localized defect passivation, excessive accumulation at the surface and grain boundaries creates nonradiative recombination pathways, promotes ion migration, triggers phase instability, and causes hysteresis.
“A monolithic two-terminal tandem architecture was realized by integrating the optimized perovskite top subcell with a passivated crystalline silicon bottom subcell,” the research's lead author, Tao Ye, told pv magazine. “This strategy not only mitigates nonradiative recombination losses but also enables superior interfacial uniformity and compositional homogeneity. Beyond achieving a high efficiency, this targeted PbI2 removal method provides a scalable and robust route to advance perovskite-silicon tandem photovoltaics, paving the way for reliable, high-performance next-generation solar energy technologies.”
A chemical polishing method using a dimethyl sulfoxide (DMSO) and chlorobenzene (CB) mixed solvent was developed to selectively remove residual PbI2 from the wide-bandgap perovskite top subcell. This approach reportedly reduced trap-state density, promoted grain boundary fusion, enhanced photoluminescence intensity, and extended carrier lifetime.
The research group treated the perovskite films with different DMSO–CB mixed solvents prepared by varying volume ratios and found that the optimal ratio was 1.6:100, which effectively removed PbI2 while maintaining surface integrity and grain compactness. Through X-ray photoelectron spectroscopy (XPS) measurements, the scientists could verify that Pb content decreased in the perovskite film after polishing. They also observed a slight binding energy shift from 138.2 eV to 138.4 eV.
“Notably, the process caused no structural damage to the perovskite lattice, highlighting its controllability and broad applicability in multilayer stacked architectures,” they explained. “This improvement in uniformity further confirmed the enhanced optoelectronic quality of the polished film.”
The tandem cell was built with a 2.5 cm x 2.5 cm bottom heterojunction (HJT) cell and a top perovskite device relying on a substrate made of indium tin oxide (ITO), a hole transport layer (HTL) made of a phosphonic acid called methyl-substituted carbazole (Me-4PACz), a perovskite absorber, a tin oxide (SnO2) buffer layer, a transparent contact made of indium zinc oxide (IZO), and a silver (Ag) metal contact.
Tested under standard illumination conditions, the tandem cell achieved a certified power conversion efficiency of 31.71%, with an open-circuit voltage of 1.839 V, short-circuit current density of 21.04 mA cm-2, and a fill factor of 81.95%. The device further exhibited suppressed hysteresis and improved operational stability, retaining over 90% of its initial power output after 700 hours of continuous simulated sunlight illumination.
“All measurements indicated that eliminating residual PbI2 effectively enhanced interfacial properties and device reliability, and underscored the efficacy of the DMSO–CB solvent system in chemical polishing,” said Ye.
The new cell design was presented in “Targeted PbI2 Removal Unlocks 31.71% Efficiency Perovskite-Silicon 2T Tandem Solar Cells,” published in RRL Solar.
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