《Energy and Environmental Sciences (IF 39.714)》Alkylammonium Ionic Liquids as Dopants in the Hole Transport Layer for Efficient and Stable Perovskite Solar Cells: Research from Professor Jangwon Seo's team at UNIST (Ulsan National Institute of Science and Technology), South Korea
Highlights
Professor Jangwon Seo’s team at UNIST (Ulsan National Institute of Science and Technology), South Korea found that:
- The researchers developed alkylammonium ionic liquids as dopants in the hole transport layer, which can achieve both doping and surface passivation for perovskite solar cells.
- Among them, octylammonium bis(trifluoromethylsulfonyl)imide (OATFSI) works best.
- OATFSI-based perovskite solar cells can achieve efficiency up to 23.34%, demonstrating good scalability.
Background
Professor Jangwon Seo’s team at UNIST pointed out that in state-of-the-art n-i-p structured perovskite solar cells, the dopant for doping the hole transport layer (HTL) is a crucial component, which affects not only the electrical properties of the HTL, but also the performance and stability of the solar cells. This study reports new bifunctional ionic liquids as dopants and surface passivators to improve the efficiency and stability of perovskite solar cells.
Results
Professor Jangwon Seo’s team at UNIST synthesized a series of alkylammonium bis(trifluoromethylsulfonyl)imide ionic liquids, including butylammonium (BATFSI), hexylammonium (HATFSI), octylammonium (OATFSI) and decylammonium (DATFSI). Among them, OATFSI has good miscibility with poly(triarylamine) solution, forming smoother HTL films and enhancing the electrical properties of HTL through effective doping. Meanwhile, OATFSI can passivate the perovskite surface in situ during spin coating of HTL. OATFSI-based perovskite solar cells can achieve efficiency up to 23.34%, owing to significantly reduced non-radiative recombination and better charge extraction.
Methods
Professor Jangwon Seo’s team at UNIST:
- Synthesized alkylammonium ionic liquids: The researchers synthesized different alkylammonium ionic liquids through chemical reaction of alkylammonium salts and bis(trifluoromethylsulfonyl)imide.
- Fabricated solar cells: The n-i-p solar cells were fabricated by depositing compact TiO2, mesoporous TiO2, perovskite active layer, poly(triarylamine) HTL with ionic liquid, and gold electrode on glass substrates.
- Characterization: XRD, UV-vis absorption spectra, TGA were used to characterize the ionic liquid materials. SEM, capacitance-voltage profiling were applied to investigate the morphology and bandgap of solar cells. Illumination curve tracer measured the power conversion efficiency.
Conclusion
In conclusion, Professor Jangwon Seo’s team at UNIST summarized that the alkylammonium ionic liquids developed in this study can not only efficiently dope the poly(triarylamine) HTL, but also passivate the perovskite surface in situ, representing a great innovation in the field of perovskite solar cells. Especially, OATFSI works best and achieves high efficiency of 23.34%. The demonstration in large area modules indicates good scalability. This study provides useful guidelines for commercialization of perovskite solar cells.
Fig. S5. (a) UPS spectra for perovskite, PTAA with or without various dopants, (b) change of
energy level for PTAA in present/absence of OATFSI, and (c) energy level alignments of
perovskite and PTAA with LiTFSI+tBP or OATFSI.
Fig. S6. UV-vis spectra of (a) pristine PTAA in film state (prepared from 10 mg ml−1 of PTAA
solution in toluene) and pristine OATFSI in solution state (9.75 mM of OATFSI in toluene) and
change of UV-Vis absorption spectra for (b) PTAA film with LiTFSI+tBP and (c-e) PTAA films
with various dopant concentrations of OATFSI under illumination
Fig. S7. (a) JSC, (b) FF, and (c) PCE statistics in box-and-whisker plots (center line: median, box
limits: upper and lower quartiles, whiskers: 1.5× interquartile range, points: outliers) of PSCs using different dopant concentrations of OATFSI
Fig. S8. XPS spectra of (a) pristine perovskite layer and perovskite layer after peeling off PTAA
film using 9.75 mM of OATFSI with (b-c) the detailed fitting curves
Fig. S11. PL transients of perovskite covered by PTAA with LiTFSI+tBP
Fig. S13. J−V curve for CBD SnO2-based PSC
Fig. S14. J−V curves of PSCs using the same concentration of alkylammonium TFSIs with
different alkyl chain lengths and commercial ionic liquid dopants
