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
a Department of Mechanical Engineering, The University of Tokyo
b Department of Materials Science and Engineering, UCLA, 420 Westwood Plaza 90095 Los Angeles
c National Institute of Advanced Industrial Science and Technology (AIST), AIST Central 5-2, Tsukuba, 305-8565, 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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