An international research team has fabricated a perovskite solar cell based on a new passivation strategy using Lewis base molecules to improve device performance.
Lewis bases are generally used in perovskite solar research to passivate surface defects in the perovskite layer. This has positive effects on energy level alignment, interfacial recombination kinetics, hysteresis behavior, and operational stability.
The scientists used Lewis base molecules based on either chalcogen-thiophene (n-Bu4S) or selenophene (n-Bu4Se), and tetra-pyridine as a bridge. They also adopted a fully encapsulated trapping tactic (FETT) to reduce perovskite surface defects. “We demonstrate that the corresponding molecules lead to a positive impact on film growth and device characteristics,” they said. “The FETT passivation remarkably improved the film morphology, carrier lifetime, and interfacial quality.”
The two Lewis base molecules have concave and flat configurations, fuse two chalcogen-containing units, and are bridged together via tetra-pyridine ligand. ”The augmented concave surface is anticipated to amplify the affinity of guest molecules for perovskite defect centers, thereby intensifying the passivation efficacy through the strategic concentration and entrapment of the associated defects,” the team explained. “Moreover, the incorporation of multiple alkyl groups at the molecular termini significantly enhanced solubility on the perovskite surface and imparted hydrophobic characteristics to the perovskite film, thereby substantially improving device stability under humid conditions.”
The group built the solar cell with a substrate made of indium tin oxide (ITO), a tin(IV) oxide (SnO₂) electron transport layer, the absorber passivized by either n-Bu4S or n-Bu4Se; a spiro-OMeTAD hole transport material, and a gold (Au) as the back electrode.
For the surface treatment of perovskite, 30 μL of n-Bu4S and n-Bu4Se solutions were spin-coated on the perovskite film at 3000 rpm for 30 s, followed by annealing at 100 C for 10 minutes.
Overall, five cells were created with n-Bu4Se passivation, five with n-Bu4S passivation, and five with no passivation for reference. On average, the reference cell achieved an efficiency of 22.57%, the n-Bu4Se reached 23.82%, and the n-Bu4S achieved a champion efficiency of 25.37% and a certified result of 25.18%.
The scientists also found that the optimal passivated device demonstrated a stable efficiency of 25.02% over 400 s, while the control device achieved an efficiency of 22.65%. Then, they tested the devices for moisture stability for 1,000 hours under a temperature of 25 C and relative humidity of 30-40%. While the control device retained 69% of its initial efficiency, the n-Bu4S passivated kept 95%.
Following that, they checked the thermal stability of the devices for 500 hours under 85 C. The control device kept 53% of its initial efficiency, and the n-Bu4S passivated kept 93%. They also placed the devices for 1,300 hours under one sun illumination and 65 C in a nitrogen gas (N₂) environment and found the reference cell kept 59.3%, and the n-Bu4S achieved 94%.
“The n-Bu4S modified devices exhibited improved operational stability under moisture, heat, and light stresses compared to its counterparts,” the academics concluded. “Therefore, this strategic design of molecular passivation is characterized by concave geometries, optimized for comprehensive encapsulation and neutralization of defect sites within perovskite films.”
The new passivation strategy was presented in “Tailoring pyridine bridged chalcogen-concave molecules for defects passivation enables efficient and stable perovskite solar cells,” published in Nature Communications. Scientists from China’s University of Electronic Science and Technology of China, Lanzhou University, and France’s French National Centre for Scientific Research (CNRS) have participated to the study.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.