Single-walled carbon nanotubes (SWNT), graphene, and fullerene (C₆₀ and PCBM) would be very efficiently used in lead halide Perovskite solar cells. A film of SWNTs or graphene can be flexible and stretchable transparent-conductive layer. At the same time, this film can be carrier-selective layers, i.e., electron-blocking-layers or hole-blocking-layers. Based on our experiences of using nanotube films for CNT-Si solar cells and organic polymer solar cells [1,2], we have explored the application of SWNT films for organic-inorganic perovskite solar cells. We have demonstrated the replacement of ITO in inverted-type perovskite solar cells, SWNTs/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al [3]. The flexible application on polyethylene terephthalate (PET) is also demonstrated [3]. With the improved perovskite structure, a film of carbon nanotubes or graphene can be practical replacement of ITO for the flexible transparent electrode of inverted perovskite solar cells [4].

Replacement of electron-blocking-layer and metal electrode in normal-type perovskite solar cells is demonstrated as well. Those devices can have comparable PCE as the conventional design with organic electron-blocking layer and top metal electrode. The normal-type perovskite solar cell, composed of ITO/C₆₀/CH₃NH₃PbI₃/SWNTs, can achieve a PCE of 17 % with spiro-MeOTAD as dopant to SWNTs [5]. This structure with a perovskite layer sandwiched by C₆₀ and SWNTs can lead to the solar cells without hysteresis and with much improved air-stability [5]. The effective passivation of the degradation of perovskite material by moisture can be achieved with C₆₀ and SWNTs [5]. More recent configuration is using a film of SWNTs for both anode and cathode electrode [6]. The new physical understanding of band alignment must be discussed based on the demonstrations of efficient carrier selective layers with these dry-deposited SWNTs which are composed of metallic and semiconductor nanotubes.

Part of this work was supported by JSPS KAKENHI Grant Numbers JP25107002 and JP15H05760.

References:

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[2] I. Jeon, C. Delacou, A. Kaskela, E. I. Kauppinen, S. Maruyama, Y. Matsuo, Sci. Rep. 6, 31348 (2016).

[3] I. Jeon, T. Chiba, C. Delacou, Y. Guo, A. Kaskela, O. Reynaud, E. I. Kauppinen, S. Maruyama, Y. Matsuo, Nano Lett. 15, 6665 (2015).

[4] I. Jeon, J. Yoon, N. Ahn, M. Atwa, C. Delacou, A. Anisimov, E. Kauppinen, M. Choi, S. Maruyama, Y. Matsuo, J. Phys. Chem. Lett., 8 (2017), 5395.

[5] N. Ahn, I. Jeon, J. Yoon, E. I. Kauppinen, Y. Matsuo, S. Maruyama, M. Choi, submitted.

[6] I. Jeon, S. Seo, Y. Sato, C. Delacou, A. Anisimov, K. Suenaga, E. I. Kauppinen, S. Maruyama, Y. Matsuo, J. Phys. Chem. C, (2017), online [DOI: 10.1021/acs.jpcc.7b10334].