Conventional perovskite solar cells (PSCs) are structured with the electron transport layer underneath the perovskite light absorbing layer and the hole transport layer on top. Although this layout has delivered strong lab performance, it faces obstacles when scaled for large area manufacturing and long term stability.
Inverted PSCs swap the positions of these two transport layers. This reversed architecture offers high power conversion potential and works well with solution based processing methods suited for large scale production, making it an appealing photovoltaic design.
Despite these advantages, inverted PSCs have been limited by problems at the bottom interface, also known as the buried interface, where the perovskite layer contacts the hole transport layer. At this hidden junction, microscopic structural irregularities and electronic defects can form, reducing both efficiency and durability over time.
Crystal-Solvate Pre-Seeding for Interface Control
To solve this issue, researchers from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences introduced a crystal-solvate (CSV) pre-seeding technique that allows precise control over this critical bottom interface. Their approach supports the development of high efficiency, large area perovskite solar modules. The findings were published in Nature Synthesis on February 27.
The process begins by depositing specially engineered low dimensional halide crystal-solvate seeds with the chemical formula PDPbI4·DMSO onto self-assembled monolayer (SAM)-modified substrates. These CSV nanocrystals serve as a structural guide for the perovskite crystals that grow afterward.
The rod-shaped CSV nanocrystals improve how well the perovskite precursor spreads across the typically water repelling SAM surface, allowing for more uniform coverage. As crystallization proceeds, the pre-deposited nanocrystals act as numerous nucleation centers, accelerating and directing the formation of the perovskite layer.
Lattice-Confined Solvent Annealing Enhances Stability
A key element of the strategy involves dimethyl sulfoxide (DMSO) molecules embedded within the CSV crystal structure. During thermal annealing, these DMSO molecules are gradually released, creating what the researchers call a “lattice-confined solvent annealing” environment at the bottom interface.
This localized solvent atmosphere promotes grain rearrangement and growth, working together with the seeded crystallization process to produce a more uniform and stable film.
“We have developed an integrated approach that simultaneously addresses crystallization regulation and interface stabilization,” said Dr. Xiuhong Sun, co-first author of the study. “This strategy delivers good performance even at buried interfaces, which are notoriously challenging to precisely control.”
High Efficiency Large Area Solar Modules
By reducing interfacial voids and smoothing grain boundary grooves, the method creates a dense and highly oriented region within the perovskite film (the perovskite “bottom layer”). This structural improvement leads to enhanced electronic properties and stronger resistance to heat and light induced stress.
The researchers also combined the CSV pre-seeding method with a slot-die coating process to fabricate a perovskite solar mini-module with an aperture area of 49.91 cm2. The device achieved a power conversion efficiency of 23.15%. The drop in efficiency from small laboratory cells to the larger mini-module was less than 3% — a result that surpasses many previously reported studies.
“This technology overcomes the longstanding scaling bottleneck caused by size effects through the combination of induced crystallization and buried interface restoration,” said Prof. Shuping Pang. “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.”