A research team led by scientists in Saudi Arabia has introduced a stabilizer-free, seed-assisted growth method to produce the pure α-phase of formamidinium lead iodide (α-FAPbI₃) perovskite.
FAPbI₃ is a prominent candidate for single-junction perovskite solar cells. However, its instability under ambient conditions typically necessitates chemical stabilizers, which can widen the bandgap and limit its photovoltaic capabilities.
Essa A. Alharbi, the corresponding author, stated, “This research presents an exciting approach to one of the biggest challenges facing FAPbI₃ perovskite solar cells: stabilizing the highly efficient α-phase without relying on compositional additives that compromise the material’s ideal bandgap.” The team has opted for a seeded-growth strategy, incorporating α-FAPbI₃ seed crystals directly into the precursor solution to facilitate crystallization, rather than using traditional stabilizers like cesium (Cs), rubidium (Rb), or methylammonium (MA).
Co-authors Nikolaos Lempesis and George Kakavelakis noted that the study merges experimental characterisation with multiscale simulations to elucidate the underlying mechanisms of seeded growth, providing a scientific basis for the remarkable efficiency and long-term stability achieved.
The research comprised two segments: experimental work and simulations. Initially, the researchers fabricated both control and seed-assisted perovskite solar cells featuring an n-i-p architecture. For the seed-assisted devices, preformed α-FAPbI₃ seeds were integrated directly into the PbI₂ precursor to guide crystallization towards the desired α-phase.
Subsequently, the target devices were produced through a second deposition step using formamidinium iodide (FAI) and methylammonium chloride (MACl), followed by annealing at 150°C for 20 minutes. The control devices were created under identical conditions but without the seeds.
Alharbi explained, “The pre-existing α-FAPbI₃ seeds lower the nucleation barrier and direct the growth of the desired photoactive α-phase while suppressing the formation of the photoinactive δ-phase. This results in highly crystalline, compact films with larger grains, fewer defects, lower surface roughness, and significantly reduced non-radiative recombination.” As a result, the devices achieved a power conversion efficiency of 23.51%, compared to 15.5% for the conventionally processed control devices, while retaining 99% of their initial performance after 3,000 hours of continuous operation under ambient conditions and one-sun illumination without encapsulation.
In the second part of the study, the researchers employed multiscale simulations to explore how the seeds affect crystallization and device performance. Density functional theory (DFT) calculations compared the energetics of α- and δ-phase growth on an existing α-FAPbI₃ seed, while molecular dynamics simulations monitored the dissolution of a 10 nm α-FAPbI₃ seed in the precursor solution, contrasting it with a seed-free solution.
Additionally, metadynamics were used to investigate nucleation pathways, and separate optical-electrical simulations evaluated the impacts of carrier mobility, lifetime, and non-radiative recombination on solar cell performance. The multiscale simulations indicated that dissolving α-FAPbI₃ seeds maintain structural motifs that preferentially encourage α-phase nucleation while inhibiting the competing δ-phase. This suggests that seeded growth not only enhances film morphology but also fundamentally modifies the crystallization pathway, resulting in fewer defects, diminished non-radiative recombination, negligible hysteresis, and improved charge transport balance.
The research team intends to expand the seeded-growth method from laboratory-scale devices to large-area perovskite solar modules using scalable sequential deposition processes. Alharbi mentioned, “We will optimise seed concentration, size, and processing conditions to ensure uniform crystallization over large substrates while maintaining high efficiency and long-term operational stability.” He concluded that the seeded-growth strategy is fully compatible with sequential deposition, making it suitable for large-area manufacturing and commercial-scale perovskite photovoltaics. This approach may also enhance other perovskite optoelectronic devices, including light-emitting diodes, where minimising defect-assisted recombination is crucial for optimal performance.
The research titled “Stabilizer-free pure α-phase FAPbI3 perovskite through seed-assisted growth yields efficient photovoltaics” was published in Materials Horizons. Contributors to the study included researchers from Saudi Arabia’s King Abdulaziz City for Science and Technology (KACST), Princess Nourah bint Abdulrahman University, Taibah University, Greece’s Foundation for Research and Technology – Hellas (FORTH), Hellenic Mediterranean University, University of Ioannina, and the UK’s University College London (UCL).
Source: pv magazine Global
