Researchers have found that a common salt can help solar cells capture more energy by giving perovskite crystals more time to grow.
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In a recent study published in the Journal of the American Chemical Society, scientists proposed using guanidinium thiocyanate (GASCN) to enhance both the efficiency and stability of perovskite solar cells. The salt, classified as a chaotropic agent, plays a surprising yet critical role in the crystallization of tin-lead halide perovskites.
Using a combination of hyperspectral imaging and real-time in situ photoluminescence spectroscopy, the team uncovered how GASCN influences crystal growth during the film formation process, particularly in the overlooked cooling stage after annealing.
The Importance of Perovskites
Perovskite solar cells have become a promising alternative to traditional silicon-based solar panels. They’re cheaper to produce, require less energy to manufacture, and offer tunable properties that allow them to capture a wider range of the solar spectrum. This flexibility makes them especially useful for tandem solar cells, which layer different materials to maximize light absorption.
In perovskite development, Sn-Pb halide compounds stand out for their adjustable band gaps, ideal for all-perovskite tandem configurations. But, producing stable, high-efficiency versions of these cells is a technical challenge, particularly due to difficulties in controlling the crystallization process.
Additives like GASCN have improved crystal quality, but the underlying photophysical mechanisms behind this have remained unclear.
Method: Salt as a Growth Modulator
To test the beneficial properties of GASCN additives, researchers added varying concentrations of the salt (5 %, 10 %, and 20 %) to Sn-Pb perovskite precursor solutions. For comparison, they also tested guanidinium iodide (GAI) and sodium thiocyanate (NaSCN).
Once prepared, the materials underwent standard characterization techniques, including scanning electron microscopy, atomic force microscopy, X-ray diffraction, and ultraviolet-visible spectroscopy. The thin films produced were then used to build perovskite solar cells, which were tested under simulated sunlight.
The researchers also used a custom in situ photoluminescence setup using a 405 nm laser to monitor how the films crystallized in real time. This was paired with steady-state and time-resolved photoluminescence measurements to evaluate optoelectronic properties such as carrier lifetimes and nonradiative losses.
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Key Findings: Slower Crystals, Better Films
They found significant signs of improvement from the GASCN addition. The simple salt slowed down the rate of crystal growth substantially, especially during the cooldown stage after annealing. Contrary to the common assumption that crystallization ends once the solvent evaporates, the team found that GASCN allowed growth to continue during this phase, resulting in smoother films with well-connected, uniform grain structures.
In situ photoluminescence data showed a transient increase in emission intensity during cooldown, suggesting enhanced film formation at this stage. This prolonged growth led to fewer defects and better structural coherence, both of which are crucial for efficient solar energy conversion.
The interaction of guanidinium cations and thiocyanate anions with the perovskite lattice helped passivate defects such as halide vacancies and undercoordinated sites. This reduced nonradiative recombination and extended charge carrier lifetimes, key indicators of high-quality films.
Device Performance: A Salt-Driven Boost
Perovskite solar cells integrated with GASCN achieved a power conversion efficiency of 22.34 %, a notable benchmark for mixed Sn-Pb perovskite devices. Beyond this relatively high efficiency, the films also showed improved stability, thanks to more controlled crystallization pathways.
In contrast, the control samples without GASCN showed rapid, uncontrolled growth during annealing, resulting in rougher films and lower performance.
The research highlights three key mechanisms behind GASCN’s success: Early nucleation during annealing, enhanced Ostwald ripening, and continued, moderated growth during cooldown. These combined effects allowed for a more energetically favorable and defect-tolerant crystal structure, ultimately boosting device performance.
Conclusion: A Simple Additive with Broad Potential
This study demonstrates how a relatively simple salt can significantly influence perovskite crystallization dynamics, resulting in more efficient and durable solar cells. GASCN improved grain size and surface uniformity, reduced defects, and extended charge lifetimes, core metrics for perovskite solar cell performance.
With efficiencies above 22 % and a clearer understanding of how additives affect crystal growth, this work paves the way for broader use of chaotropic agents in perovskite engineering. Future studies may focus on other similar compounds, such as imidazolium salts, urea derivatives, or sulfonic acid-based agents, to further optimize tandem solar cell designs.
Journal Reference
Dong, Y., et al. (2025). Crystal Growth Modulation of Tin-Lead Halide Perovskites via Chaotropic Agent. Journal of the American Chemical Society. DOI: 10.1021/jacs.5c05772. https://pubs.acs.org/doi/10.1021/jacs.5c05772
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