Highly Stable and Efficient 2D/3D Formamidinium-Lead-Iodide Inverted-Type Perovskite Solar Cells

Abhishek Thote^a, Il Jeon^a, Yang Yang^b, Shigeo Maruyama^a^,^c, Yutaka Matsuo^a, Hirofumi Daiguji^a

^aUniversity of Tokyo, Japan, Japan

^bDepartment of Materials Science and Engineering, UCLA, 420 Westwood Plaza 90095 Los Angeles

^cNational Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 1-1-1 Higashi, Ibaraki, Japan

Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference on Perovskite and Organic Photovoltaics and Optoelectronics (IPEROP19)

Kyōto-shi, Japan, 2019 January 27th - 29th

Organizers: Hideo Ohkita, Atsushi Wakamiya and Mohammad Nazeeruddin

Oral, Abhishek Thote, presentation 024
DOI: https://doi.org/10.29363/nanoge.iperop.2019.024
Publication date: 23rd October 2018

Organic-inorganic lead halide perovskite solar cells (PSCs) have attracted a great deal of attention owing to the high absorption coefficient, low fabrication cost, and flexible applications. The high absorption arises from a suitable bandgap of perovskite materials, which is close to the Shockley–Queisser limit of 1.4 eV. FAPbI₃ is potentially more suitable as an active material than MAPbI₃ for PSCs since FA-based lead iodide perovskite (FAPbI₃) has been reported to possess an ideal band gap of 1.4 eV, which translate to the sunlight absorption up to ca.886 nm. However, pure FAPbI₃ has been reported to exhibit low stability for its trigonal α-phase is sensitive to humidity, and readily turns into a non-photoactive hexagonal δ-phase at room temperature. Although more thermally and structurally stable FAPbI₃ has been realized through partial substitution of FA by Cs (FACsPbI₃), the stability should be improved further. Recently, we reported 2D perovskite-added FACsPbI₃ (2D/3D FACsPbI₃) where the 2D PEA-based perovskite protects the 3D grains from α to δ phase transition. 2D/3D FACsPbI₃-based PSCs in a normal-type structure gave a certified efficiency of PCE of 19.8%with a remarkable stability.

Even though normal-type PSCs give higher PCEs, inverted-type PSCs provides a wider selection of flexible substrates along with reduced hysteresis and improved device stability under UV illumination. Thus far, a limited study on FAPbI₃–based inverted-type PSCs has been reported. We investigated 2D/3D FACsPbI₃ in inverted-type PSCs and discovered that they show higher stability and reproducibility than the normal-type devices. The higher stability came from reduced trap-charge at interface, hydrophobicity of poly(triarylamine) (PTAA), and exclusion of 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-MeOTAD). The higher reproducibility came from the elastic nature of PTAA charge carrier layer, onto which brittle 2D/3D FACsPbI₃ film is being spin-coated, compared to hard and brittle SnO₂ for normal-type PSCs. The strain caused by both 2D perovskites at grain boundaries and the big size of FA led to 2D/3D FACsPbI₃ being liable to forming cracks. We investigated the relationship between the mechanical property the films with the device reproducibility, the energetics of the 2D/3D FACsPbI₃ films in inverted-type PSCs, and the origin of the phase stability of 2D/3D FACsPbI₃. The inverted-type 2D/3D FACsPbI₃ PSCs gave a PCE of 18.2% with a greater stability and higher reproducibility than the normal type PSCs.

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