Lewis-Acid Doping of Triphenylamine-Based Hole Transport Materials Improves the Performance and Stability of Perovskite Solar Cells

by Jiang Liu, Wenzhu Liu, Erkan Aydin, George T. Harrison, Furkan H. Isikgor, Xinbo Yang, Anand S. Subbiah, Stefaan De Wolf
Research Article Year: 2020

Bibliography

Liu, J., Liu, W., Aydin, E., Harrison, G. T., Isikgor, F. H., Yang, X., Subbiah, A. S., De Wolf, S. (2020). Lewis-Acid Doping of Triphenylamine-Based Hole Transport Materials Improves the Performance and Stability of Perovskite Solar Cells. ACS Applied Materials & Interfaces.

Extra Information

This study, which came out in the recent issue of ACS Applied Materials & Interfaces, successfully demonstrates the Lewis-acid (TPFB) doping of the widely used spiro-OMeTAD hole transport materials for perovskite solar cells to. This dopant replaces the conventional LiTFSI/tBP doping. By doing so, the device stability is increased and processing is simplified.

Abstract

Highly efficient perovskite solar cells (PSCs) fabricated in the classic n–i–p configuration generally employ triphenylamine-based hole-transport layers (HTLs) such as spiro-OMeTAD, PTAA, and poly-TPD. Controllable doping of such layers has been critical to achieve increased conductivity and high device performance. To this end, LiTFSI/tBP doping and subsequent air exposure is widely utilized. However, this approach often leads to low device stability and reproducibility. Departing from this point, we introduce the Lewis acid tris(pentafluorophenyl)borane (TPFB) as an effective dopant, resulting in a significantly improved conductivity and lowered surface potential for triphenylamine-based HTLs. Here, we specifically investigated spiro-OMeTAD, which is the most widely used HTL for n–i–p devices, and revealed improved power conversion efficiency (PCE) and stability of the PSCs. Further, we demonstrated the applicability of TPFB doping to other triphenylamine-based HTLs. Spectroscopic characterizations reveal that TPFB doping results in significantly improved charge transport and reduced recombination losses. Importantly, the TPFB-doped perovskite devices retained near 85% of the initial PCE after 1000 h of storage in the air, while the conventional LiTFSI-doped device dropped to 75%. Finally, we give insight into utilizing other similar molecular dopants such as fluorine-free triphenylborane and phosphorus-centered tris(pentafluorophenyl)phosphine (TPFP) by density functional theory analysis underscoring the significance of the central boron atom and fluorination in TPFB for the formation of Lewis acid–base adducts.

Keywords

Perovskite triphenylamine Lewis acids doping stability