FAPbI3 Perovskite Crystallization for Stable Alpha-Phase Films
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Solution Overview
Problem
The inefficiency in commercialization of perovskite solar cells is attributed to the challenge of achieving dense, uniform, and well-crystallized large-area perovskite films, which are prone to phase transitions from the photoactive α-phase to the photo-inactive δ-phase, leading to microstructural defects and reduced performance and stability, especially in humid environments.
Innovation Solution
A method involving the use of a perovskite precursor solution with a mole ratio of FA:Pb greater than 0.85, an ionic liquid with a cationic imidazole derivative linked to a carbon chain bearing a cyano group, and vacuum drying followed by annealing to form α-phase FAPbI3-based perovskite films, promoting direct transition to the desired α-phase without intermediate phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional crystallization methods are used for FAPbI3-based perovskite, then the perovskite film can be formed, but phase transition from photoactive α-phase to photo-inactive δ-phase occurs leading to microstructural defects and reduced performance
Solution Approach 1:
The patent introduces an ionic liquid as an intermediary substance during the crystallization process. This ionic liquid mediates the phase transition from δ-phase to α-phase, enabling controlled formation of the photoactive black phase without passing through deleterious intermediate phases. The ionic liquid acts as a temporary facilitator that guides the crystallization pathway toward the desired stable α-phase structure.
Solution Approach 2:
The patent modifies the crystallization parameters by controlling the composition ratio of FA:Pb greater than 0.85 and using specific ionic liquid concentrations (0.6 to 1.0 mol%). These parameter changes shift the phase stability landscape, enabling direct transition to the α-phase at room temperature and high humidity conditions where conventional methods fail.
2Manufacturing precision
If vacuum drying and annealing are used to form perovskite films, then film density is improved, but phase purity and crystalline quality may deteriorate without proper control
Solution Approach 1:
The patent applies preliminary action by incorporating the ionic liquid into the precursor solution before deposition. This preliminary incorporation ensures that the ionic liquid is present during the entire crystallization process, including vacuum drying and annealing steps, thereby guiding phase formation from the outset and preventing phase impurities during subsequent thermal processing.
3Productivity
If FAPbI3-based perovskite is used for high efficiency, then photovoltaic performance is improved, but stability in humid environments deteriorates due to phase transition
Solution Approach 1:
The patent changes the compositional parameters by using FA:Pb ratio greater than 0.85 and introducing ionic liquid at specific concentrations. These parameter changes stabilize the α-phase structure thermodynamically, allowing the perovskite to maintain its photoactive black phase even under high humidity conditions (95% relative humidity) and room temperature, thereby achieving both high efficiency and improved stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in high-crystallinity, pinhole-free films with enhanced photovoltaic efficiencies and increased stability, achieving efficiencies exceeding 20% and maintaining operational stability for 1000 hours with minimal trap densities and phase segregation.
Implementation Method 1
promoting direct transition to the desired α-phase without passing through the transitions to deleterious intermediate phases
Implementation Method 2
vacuum drying followed by annealing to form α-phase FAPbI3-based perovskite films
Implementation Method 3
vacuum drying followed by annealing to form α-phase FAPbI3-based perovskite films
Data Source
Figure 1(a)~1(c)
Figure 2A~3
Figure 4A~4C
AI summary
The present invention relates to a method for preparing an α-phase FAPbI3-based perovskite film, wherein FA is formamidinium [CH(NH2)2]+, comprising the following steps: (1) preparing a perovskite precursor solution containing (a) perovskite precursors FAI and PbI2 with a mole ratio FA:Pb of more than 0.85, and preferably from 0.90 to 1.00, and (b) an ionic liquid of formula AB, wherein A is a cationic imidazole derivative in which at least one of the two nitrogen atoms in the imidazole ring is linked to a carbon chain bearing a cyano (-C≡N) group and B is an anion; (2) spin coating the perovskite precursor solution onto a substrate in an inert atmosphere to prepare a spin coated film; (3) vacuum drying the spin coated film to form a fresh perovskite film; and (4) annealing the fresh perovskite film to form the α-phase FAPbI3-based perovskite film.