A group of researchers led by China’s Soochow University has engineered a dual-molecule interface layer for inverted perovskite solar cells by coassembling two carbazole-based molecules to control interfacial chemistry and structure. This design reportedly locks molecular ordering, reduces defects and stress, and enables more efficient charge extraction for highly efficient and stable solar cells.
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 researchers explained that the dual-molecule approach was intended to suppress interfacial defects and chemical instability at the perovskite/transport layer boundary by improving molecular ordering and passivation. It also aimed to enhance charge extraction while reducing nonradiative losses.
Their strategy consisted of adding 9H-carbazol-2-yl trifluoromethanesulfonate (CzOTf) to the hole transport layer (HTL) made of commonly used phosphonic acid called methyl-substituted carbazole (Me-4PACz). Instead of replacing the existing HTL, CzOTf is coassembled with Me-4PACz at the nickel oxide (NiOx)/perovskite interface, where it integrates into the molecular monolayer structure.
This addition enables complementary functions: Me-4PACz maintains efficient hole-selective contact and anchoring to NiOx, while CzOTf enhances molecular packing, increases surface coverage, and introduces additional chemical functionality through its sulfonate group. Together, they form a more uniform and strongly interacting interfacial layer that simultaneously improves electronic coupling, defect passivation, and interfacial stability.
“As shown by the scanning electron microscopy (SEM), the Me-4PACz–based control perovskite exhibits pervasive pinhole defects and discontinuities at the bottom interface,” the research team explained. “In contrast, the CzOTf-modulated film forms a substantially denser, more compact, and pinhole-suppressed interfacial layer.”
“CzOTf not only densifies the buried interface but also facilitates perovskite crystallization on top of the modulated contact, in agreement with the SEM observations and confirming its beneficial role in buried-interface engineering,” the academics went on to say. “CzOTf modulation in the Me-4PACz sample induces a less negative slope, unambiguously confirming that CzOTf incorporation promotes tensile-stress release in the perovskite film.”
The device adopts a standard n–i–p inverted architecture, starting from a fluorine-doped tin oxide (FTO) transparent conductive substrate coated with a NiOx hole transport layer modified by a coassembled Me-4PACz+CzOTf interfacial layer. On top, the perovskite absorber is deposited as the active layer, followed by a fullerene (C60) electron transport layer to facilitate electron extraction. A thin bathocuproine (BCP) buffer is then used to improve electron selectivity and protect the underlying layers, before completing the stack with a thermally evaporated silver (Ag) back electrode.
Tested under standard illumination conditions, the cell achieved a power conversion efficiency of 27.3%, an open-circuit voltage of 1.185 V, a short-circuit current density of 26.30 mA cm², and a fill factor of 87.64%. A reference device built without the dual molecule approach achieved an efficiency of 26.20%, an open-circuit voltage of 1.172 V, a short-circuit current density of 26.05 mA cm², and a fill factor of 85.79%.
The CzOTf-modified perovskite cell were then scaled up to a 766 cm² active area, demonstrating a power conversion efficiency of 21.54%, an open-circuit voltage of 50.93 V, an short-circuit current of 0.4040 A, and a fill factor of 80.20%.
“The CzOTf-modulated perovskite solar cerlls retain 92% of their initial efficiency after 2000 hours of continuous light soaking,” the scientists stated. “The CzOTf-modulated large-area module operated stably outdoors for 35 days without degradation.”
The novel cell architecture was presented in “Unlocking 27.3% perovskite photovoltaics by interface-locked dual-molecule contact,” published in ScienceAdvances.
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