Single-Walled Carbon Nanotubes and Hetero-Nanotubes for Perovskite Solar Cells

Abstract

Single-walled carbon nanotubes (SWCNT), graphene, and fullerene (C60 and PCBM) are very efficiently used in organic-inorganic Perovskite solar cells [1,2]. A film of carbon nanotubes or graphene can be the practical replacement of ITO for the flexible transparent electrode of inverted perovskite solar cells [3]. 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)/SWCNTs. The use of SWCNT as the top electrode instead of metal electrode is also enhances the stability of PSCs by removing the metal-ion migration, and considerably reduces the fabrication cost, and suitable for the development of tandem system. The normal-type perovskite solar cell, composed of ITO/C60/MAPbI3/SWCNTs, can achieve a PCE of 17 % with spiro-MeOTAD as dopant (or HTL) to SWCNTs [4]. The better performance of solar cells can be obtained by tuning of energy level of SWCNT with Trifluoromethanesulfonic acid (TFMS) doping. For 2D/3D FACsPbI3 system we have reached PCE of 17.6% [5]. Recently, we have developed further by using high concentration of hole-transporting material [6]. For MAPbI3 system, we have obtained the highest PCE of 18.8%. This PCE is higher than that of the metal electrode-based control devices, which gave a PCE of 18.1%.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 single-walled carbon nanotube (SWCNT); SWCNT@BNNT. Then, the further coating of coaxial MoS2 nanotubes results SWCNT@BNNT@MoS2NT. The inner SWCNT and outer MoS2NT are electrically coupled through a few layer BNNT. This new structure shown in Fig. 1 is expected to give extra functionality, durability in the solar cell devices.Part of this work was supported by JSPS KAKENHI Grant Numbers JP15H05760, JP18H05329.