Single-Walled Carbon Nanotubes and Hetero-Nanotubes for Perovskite Solar Cells
Authors: Maruyama Shigeo 
Published: July 2021

Single-walled carbon nanotubes (SWCNTs), graphene, and fullerene (C60 and derivatives) are very efficiently used in organic-inorganic Perovskite solar cells [1, 2]. A film of carbon nanotubes or graphene can be the practical replacement [3] of ITO for the flexible and/or foldable [4] transparent electrode of inverted perovskite solar cells. Doping of SWCNT is essential for high performance solar cells through increased in-plane film conductivity and energy level adjustment. Since p-doping is easier than n-doping, it is more practical to use SWCNT electrode in the hole-transport side. Hence, we have developed the normal type perovskite solar cells composed of ITO/ETL/MAPbI3/HTL-SWCNT. The use of SWCNT as the top electrode instead of metal enhances the stability of PSCs by removing the metal-ion migration, and considerably reduces the fabrication cost, and is suitable for the development of tandem system. Recently, we have improved the performance with higher concentration of hole-transporting material [5]. For MAPbI3 system, we have obtained the highest PCE of 18.8 % compared with the control device with gold electrode with PCE of 18.1%. Because of transparency of SWCNT film is higher than that of ITO in the NIR region, SWCNT electrode based perovskite–silicon tandem solar cells can have better performance than ITO-based one [6]. In addition to our demonstration of 24.4 % total PCE in our previous work [6], we are now demonstrating the higher preliminary PCE of 27.7 %.
Finally, the ultimately inorganic stable doping of SWCNT could be possible by using the one-dimensional van der Waals hetero-nanotubes [7]. We have synthesized the coaxial few-layer hexagonal boron nitride nanotube (BNNT) around a SWCNT; SWCNT@BNNT. Then, the further coating of coaxial MoS2 nanotubes results SWCNT@BNNT@MoS2NT as shown in Fig. 1. The inner SWCNT and outer MoS2NT are electrically coupled through a few layer BNNT. The preliminary PSC device using the heteronanotube film shows the advantage [8].
Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.
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Figure 1