Publication date: 4th October 2024
Perovskite solar cells (PSCs) have attracted worldwide attention due to their high power conversion efficiency (PCE) and low-cost solution processing. Besides the film and interfacial engineering of the perovskite layer, the development of hole-collecting materials (HCMs) is a critical key to boosting the performance of PSCs.
In inverted PSCs, the use of chemically adsorbed monolayers that can efficiently collect photo-generated holes from the perovskite layer and transport them to a transparent conducting oxide (TCO) electrode as the hole-collecting layer (HCL) has become one of the mainstream directions.[1]
Recently, we developed a tripodal molecule composed of a triazatruxene core connected with three phosphonic acid anchoring groups (PATAT).[2] We demonstrated that after being chemically adsorbed on the TCO surface, PATAT molecules tend to form a monolayer with a face-on orientation, resulting in improved hole-collection compared to their monopodal counterpart, and the corresponding inverted PSCs using the PATAT monolayer as HCL exhibited PCEs up to 23%. However, PATAT still has its own drawbacks that need to be improved, such as its difficulty in further functionalization and the hydrophobicity of its monolayer.
In this work, we designed a series of isotriazatruxene derivatives bearing three phosphonic acid anchoring groups, iso-PATAT and its tribromo-substituted analogue, iso-PATAT-Br, as hole-collecting monolayer materials. Isotriazatruxene is an isomer of triazatruxene, which has two indole moieties facing each other, leading to a steric hindrance when bulky substituents such as alkyl phosphonic acid groups were introduced into –NH positions. Taking advantage of this point, after being chemically adsorbed, instead of binding to the TCO surface, some phosphonic acid groups would point upward, leading to a hydrophilic monolayer and improved surface wettability.
Inverted PSC devices using these iso-PATAT molecules as hole-collecting monolayers were fabricated and evaluated. Iso-PATAT-Br-based PSCs exhibited superior performances with PCEs up to 25.2%, which is higher than the devices fabricated with our previously reported PATAT (PCE = 25.0%) under the same condition.
In this presentation, molecular design, characterization, and device evaluation will be discussed in detail.
We thank Mr. Aruto Akatsuka and Prof. Hiroyuki Yoshida (Chiba University) for UPS and MAES measurements. We also thank Dr. Takumi Yamada and Prof. Yoshihiko Kanemitsu (ICR, Kyoto University) for PL and TRPL measurements.
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