Regular perovskite solar cells (PSCs)—which place the electron-transport layer beneath the perovskite absorber and the hole-transport layer on top—have limitations with respect to large-scale manufacturing and stability. In contrast, inverted PSCs—which reverse the positions of the electron- and hole-transport layers—boast high power conversion potential and good compatibility with scalable solution processing techniques, making them a promising photovoltaic technology.
Unfortunately, the performance and long-term stability of inverted PSCs have long been constrained by unregulated microscopic structures and electronic defects at the critical bottom interface, defined as the buried interface, where the perovskite layer interfaces with the hole-transport layer.
To address this problem, a research team from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences has developed a crystal-solvate (CSV) pre-seeding method that enables precise regulation of the bottom interface, paving the way for the development of high-efficiency, large-area perovskite photovoltaic modules.
The study was published in Nature Synthesis on February 27.
The new method involves pre-depositing custom-designed low-dimensional halide crystal-solvate seeds—with the chemical formula PDPbI4·DMSO—on self-assembled monolayer (SAM)-modified substrates. These CSV nanocrystals act as a structural template for the subsequent growth of perovskite crystals.
The anisotropic, rod-shaped CSV nanocrystals significantly enhance the wettability of the hydrophobic SAM surface, ensuring the uniform spreading of the perovskite precursor solution. Notably, during the crystallization process, these pre-seeded nanocrystals serve as abundant heterogeneous nucleation sites, thereby effectively accelerating the formation of perovskite crystals.
A core innovation of the strategy lies in the dimethyl sulfoxide (DMSO) solvent molecules locked within the CSV crystal structure. During thermal annealing, these molecules are released in a controlled manner, creating a novel "lattice-confined solvent annealing" microenvironment at the bottom interface. This mild in situ solvent atmosphere facilitates grain reorganization and growth, forming a synergistic effect with seed-induced crystallization.
"We have developed an integrated approach that simultaneously addresses crystallization regulation and interface stabilization," said Dr. SUN Xiuhong, co-first author of the study. "This strategy delivers good performance even at buried interfaces, which are notoriously challenging to precisely control."
The new technology eliminates interfacial voids and smooths grain boundary grooves, while ultimately producing a dense, highly oriented region of the perovskite film (the perovskite "bottom layer") with significantly improved electronic properties and photothermal stability.
Additionally, the team integrated the CSV pre-seeding strategy with a slot-die coating process, successfully fabricating a perovskite solar mini-module with an aperture area of 49.91 cm² that achieves a high power conversion efficiency of 23.15%. Importantly, the efficiency loss between small-area cells and the mini-module is less than 3%—a figure that outperforms many previously reported results.
"This technology overcomes the longstanding scaling bottleneck caused by size effects through the combination of induced crystallization and buried interface restoration," said Prof. PANG Shuping. "Beyond its direct application in perovskite photovoltaics, the crystal-solvate pre-seeding concept establishes a versatile material platform: By tuning organic cations and solvent molecules, a diverse library of CSV materials can be designed, opening up a new paradigm for interface engineering in perovskite photovoltaics and other soft-lattice semiconductor optoelectronic devices alike."
