Researchers use guanidinium thiocyanate to raise perovskite cell efficiency

Researchers have used guanidinium thiocyanate as a chaotropic agent to modulate the crystal growth rate during perovskite crystallization. They compared different concentrations of the guanidinium thiocyanate. Champion device efficiency was 22.34%.

A research team led by scientists from the University College London in the United Kingdom has utilized simple salt to enhance the performance of tin-lead (Sn−Pb) perovskite solar cells. The salt, guanidinium thiocyanate (GASCN), was used as a chaotropic agent that modulated the crystal growth rate during perovskite crystallization.

“Our approach provides a straightforward, effective way to enhance perovskite quality during manufacturing, delivering solar cells that are both higher performing and more stable, key requirements for commercial success,” said corresponding author Tom Macdonald in a statement issued by the university. Co-author Chieh-Ting Lin added that “it opens the door to fine-tuning the structure of perovskites for high-performance tandem solar cells, with the potential to significantly push the limits of efficiency.”

Chaotropic agents such as GASCN, the team explained, disrupt the structure of secondary bonds such as Lewis acid−base interactions in the precursor solution. Different GASCN concentrations were tested in this research, namely 5%, 10% and 20%. They were applied to Sn−Pb perovskite, typically the bottom layer of a tandem cell. In addition, a reference cell, with 0% of GASCN, was also tested, along with two other additives, namely guanidinium Iodide (GAI) and sodium thiocyanate (NaSCN).

“We used a one-step antisolvent technique to deposit a narrow-bandgap mixed Sn–Pb perovskite, Cs₀.₀₂₅FA₀.₄₇₅MA₀.₅Sn₀.₅Pb₀.₅I₂.₉₂₅Br₀.₀₇₅. We prepared the precursor solution by adding a stoichiometric blend of the chemicals in a solvent mixture of dimethylformamide and dimethyl sulfoxide (DMF/ DMSO),” the academic explained. “To modify these perovskite films, we introduced GASCN at different molar ratios with respect to the perovskite molar concentration.”

The total device active area of the single-junction cell was 0.18 cm2, and the mask aperture area was 0.1 cm2. Its structure consisted of glass as substrate, indium tin oxide (ITO) as transparent conducting electrode, poly (3,4-ethylenedioxythiophene)−poly (styrenesulfonate)  (PEDOT:PSS) as the hole transport layer (HTL), Sn–Pb perovskite as light absorber, fullerene (C₆₀) as electron transport layer (ETL), bathocuproine (BCP) as a buffer layer an silver (Ag) as tp electrode. That resulted in a structure of glass/ITO/PEDOT:PSS/perovskite/C60/BCP/Ag.

“The champion control devices achieved a power conversion efficiency (PCE) of 19.12%, short-circuit current density (Jsc) of 30.92 mA cm−2, open-circuit voltage (Voc) of 0.81 V, and a fill factor (FF) of 76.29%. In contrast, devices with 10% GASCN showed a PCE of 22.34%, a Jsc of 31.84 mA cm−2, a Voc of 0.87 V, and an FF of 80.02%,” the results showed. “All PV parameters systematically improved as the GASCN concentration increased from 0% to 10% but declined when the concentration went further to 20%.”

While the champion device treated with GASCN achieved the highest PCE of 22.34%, the one treated with GAI achieved 15.4%, and the one using NaSCN got 18.13%. To further explore the origin of the high performance of the GASCN addition, the team employed in situ photoluminescence (PL) to observe the perovskite crystallization process in real time.

“This work gave us valuable insight into the crystal formation process. By modulating it in a controlled way, we were able to create much higher-quality films – a change that directly translates into more efficient and longer-lasting devices,” first author Yueyao Dong said. “Real-time in situ PL measurements revealed that GASCN slowed the crystal growth rate and promoted the formation of homogeneous and high-quality perovskite films. Notably, the transient increase in PL intensity during the cooldown process underscored the critical importance of this often-overlooked stage in determining the final optoelectronic properties of the films,” the team added.

They presented the results in “Crystal Growth Modulation of Tin−Lead Halide Perovskites via Chaotropic Agent,” published in the Journal of the American Chemical Society. Researchers from the University College London, Queen Mary University of London, London South Bank University, National Chung Hsing University in Taiwan, and the University of Washington in the United States have participated in the study.