Engineering the Central Heteroatom of Hole Transporting Enamines for Efficient Perovskite Solar Cells
Deimante Vaitukaityte a, Minh Anh Truong b, Kasparas Rakstys a, Richard Murdey b, Vygintas Jankauskas c, Vytautas Getautis a, Atsushi Wakamiya b
a Department of Organic Chemistry, Kaunas University of Technology, Lithuania
b Institute for Chemical Research, Kyoto University, Japan
c Institute of Chemical Physics, Vilnius University, Lithuania
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Deimante Vaitukaityte, 218
Publication date: 20th April 2022

Stabilization of the efficient perovskite solar cells (PSCs) using a low-cost and simply affordable hole transporting materials (HTMs) has been identified as a current challenge. HTMs are irreplaceable components, which help to improve efficiency of hole extraction and reverse electron flow blocking. In a regular PSC with n-i-p structure HTM spiro-OMeTAD is routinely employed as highly efficient reference material [1]. Although PSCs have recently reached certified power conversion efficiency (PCE) of 25.7%, there is a renewed interest to engineer new HTMs, which can help to exceed the currently certified PCE.

In this work, four HTMs containing different central heteroatoms leading to multi-armed enamines were synthesized by a simple and straightforward condensation reaction, which in contrary to spiro-OMeTAD does not require expensive palladium catalysts and water is the only by-product. In addition, simple product workup and purification may result in significantly reduced synthesis costs.

To investigate photoelectrical properties of synthesized HTMs hole drift mobility (µ) and ionization potential (IP) were measured. Solid-state IP was measured using the electron photoemission in the air (PESA) to study the HOMO energy level of novel enamines. The results demonstrated that the central atom significantly influences the HOMO level, the N-containing compound V1435 showed the highest-lying HOMO level of 5.27 eV, while other HTMs containing less electron rich central atom showed lower levels (O-V1433, S-V1434, and C-V1431 (5.37<5.52<5.54 eV), respectively). Charge transport properties of the investigated HTMs were measured using xerographic time-of-flight (XTOF) technique. V1435 exhibited the highest zero-field hole drift mobility (µ0) among the series having the value of 2.0 × 10-5 cm2 V-1 s-1, while the other enamines demonstrated one order of magnitude lower hole drift mobility.

n-i-p solar cells were fabricated with the device layout ITO/SnO2/perovskite/HTM/Au to test novel materials as hole transporting layers. The device containing HTM V1435 exceeded a photovoltaic performance of 20% outperforming commercial spiro-OMeTAD. In addition, this is the highest registered efficiency comparing to our previously published enamine-based HTMs.

VG and DV acknowledge funding from the Research Council of Lithuania under grant agreement Nr. 01.2.2-LMT-K-718-03-0040 (SMARTMOLECULES).

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