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A team of Chinese researchers has modified the absorber of a conventional perovskite solar cell with potassium trifluoromethanesulfonate (KTFS) and found that the additive improved the performance and stability of the device. The cells perovskite film had fewer lead defects and lower JV hysteresis.
Researchers at Chinas Hangzhou Dianzi University have fabricated a perovskite solar cell with a multifunctional additive known as potassium trifluoromethanesulfonate (KTFS), which they claim can significantly reduce lead vacancy defects in the perovskite film.
“The KTFS molecule is a typical type of potassium salt that includes cationic potassium (K+) and anionic trifluoromethanesulfonate (SO3CF3-), indicating a bifunctional interaction between KTFS and perovskite,” they explained. “The sulfonyl group can passivate the subcoordinated lead of the deep-level defect and thus inhibit nonradiative recombination.”
In the study “ Modulating vacancy-related defects and hole extraction via a multifunctional additive for high-performance perovskite solar cells ,” published In Cell Reports Physical Science , the research group described the results of the proposed additive based on potassium salts, as it provides better surface morphology and greater crystallinity in a film constructed with a layer of lead iodide (PbI2) treated with KTFS by thermal annealing.
The performance of the KTFS-modified film was compared to that of a control perovskite film without the additive, and the former was found to have less lead impurities than the control film. “The presence of Pb impurities in perovskite films is a result of the decomposition of residual PbI2 when exposed to light or X-ray irradiation, indicating an iodine deficiency in the films,” the academics note. “These metallic lead clumps act as impurities, which can accelerate the degradation of perovskite films and affect the stability of perovskite solar cells.”
Furthermore, it was found that KTFS did not affect the 1.52 eV energy band gap of the formamidinium lead iodide perovskite (FAPbI3) material selected for the film.
The group built the solar cell with an indium tin oxide (ITO) substrate, an electron transport layer (ETL) based on tin oxide (SnO2), the KTFS-modified perovskite absorber, a holes (HTL) based on Spiro-OMeTAD and a silver (Ag) metal contact.
Tested under standard lighting conditions, the device achieved a power conversion efficiency of 23.96%, an open circuit voltage of 1.165 V, a short circuit current density of 25.29 mA/cm2, and a fill factor of 81.33%. In comparison, a reference device without KTFS achieved an efficiency of 22.23%, an open circuit voltage of 1.15 V, a short circuit current density of 25.03 mA/cm2, and a fill factor of 77. 24%.
“The KTFS-modified device shows a relatively low hysteresis index, with a value of 4% compared to 6.8% for the control device,” the scientists say. “It is speculated that the existence of K+ in the KTFS incorporated into the perovskite may inhibit ion migration, thus reducing the JV hysteresis.”
The group also discovered that the KTFS-modified cell was able to maintain 90% of its original efficiency after 1,200 h of storage, while the control device only reached 80%. |
