Aniline-based Enamine Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

Deimante Vaitukaityte^a, Zhiping Wang^b, Tadas Malinauskas^a, Artiom Magomedov^a, Giedre Bubniene^a, Vygintas Jankauskas^c, Vytautas Getautis^a, Henry Snaith^b, Egidijus Kamarauskas^c

^aDepartment of Organic Chemistry, Kaunas University of Technology, Radvilenu 19, 50254, Kaunas, Lithuania

^bUniversity of Oxford, Department of Physics, Clarendon Laboratory, UK, Parks Road, United Kingdom

^cDepartment of Solid State Electronics, Vilnius University, Saulėtekio 9, Vilnius, 10222, Lithuania

International Conference on Hybrid and Organic Photovoltaics
Proceedings of Online International Conference on Hybrid and Organic Photovoltaics (OnlineHOPV20)

Online, Spain, 2020 May 26th - 29th

Organizers: Tracey Clarke, James Durrant, Annamaria Petrozza and Trystan Watson

Poster, Deimante Vaitukaityte, 062
Publication date: 22nd May 2020

ePoster:

Most of the high efficiency n-i-p structured perovskite solar cells (PSCs) are based on Spiro-OMeTAD hole transporting material (HTM), which is very expensive [1]. The high cost is mainly generated by the multi-step synthesis, complicated purification procedures and use of transition metal catalysts [2]. The aim of this work is to functionalize low-cost enamines via single-step synthetic procedure from commercially available aniline precursors without the use of expensive and problematic organometallic catalysts. Enamines with two (V1092) or three (V1091) diphenylethenyl groups were isolated depending on the ration of the reagents. Additionally, aniline derivative with methoxy group in para-position (V1056) and 3,5-dimethyl substituted analogue (V1102) were also used for the synthesis.

Photoelectron spectroscopy in air method was used to measure ionization potential (I_p). Aniline derivative V1092 exhibits the highest ionization energy (5.3 eV). Additional electron donating diphenylethenyl (V1091) or methoxy (V1056) group lowers I_p of the HTM by ~0.1 eV. On the whole, the investigated HTMs show slightly higher ionization energy than Spiro-OMeTAD (5.0 eV), but still suitable for the hole extraction in PSCs. Charge transport properties of the investigated HTMs were measured using xerographic time-of-flight technique. V1056 shows a similar hole mobility (7.8×10^-4 cm²/Vs) as compared to Spiro-OMeTAD (5.0×10^-4 cm²/Vs). In contrast, V1091 displays significantly better hole drift mobilities (1.7×10^-2 cm²/Vs) at high electric fields. The addition of the methyl groups at 3,5-positions of the phenyl ring in V1102 results in reduced charge mobility (1.5×10^-4 cm²/Vs).

The materials were tested as hole transporting layers (HTLs) in planar heterojunction PSCs. The device using V1102 and V1056 shows a champion efficiency of 17.6% and 18.7%, respectively, which is slightly lower than the power conversion efficiency of 20.2% for the control device using Spiro-OMeTAD. In contrast, the PSC using V1091 exhibits a high efficiency of 20.2%. To access device stability non-encapsulated high efficiency devices were aged with V1091 and Spiro-OMeTAD HTLs in ambient air with a relative humidity of ~ 45% under dark conditions. V1091 device shows superior stability sustaining 96% of its original efficiency after 820 h. In contrast, stabilized power output of the control device drops to 42% after aging.

References:

[1] Rakstys, K.; Igci, C.; Nazeeruddin, M. K. Efficiency vs. stability: dopant-free hole transporting materials towards stabilized perovskite solar cells. Chem. Sci. 2019, 10, 6748-6769.

[2] Vaitukaityte, D.; Wang, Z.; Malinauskas, T.; et al. Efficient and Stable Perovskite Solar Cells Using Low‐Cost Aniline‐Based Enamine Hole‐Transporting Materials. Adv. Mater. 2018, 30, 45, 1803735.

Acknowledgements:

D. Vaitukaityte acknowledges funding from the European Union`s Horizon 2020 research and innovation programme under grant agreement No. 763977 of the PerTPV project and Research Council of Lithuania (grant No. MIP-17-70).

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