Utilizing the Dip Coating Method to Prepare Uniform Contact Materials for Perovskite Solar Cells
Jan-Henrik Smått a, Muhammad Talha Masood a, Syeda Qudsia a, Simon Sandén b, Oskar J. Sandberg b, Mathias Nyman b, Paola Vivo c, Peter D. Lund d, Ronald Österbacka b
a Åbo Akademi University, Finland, Porthaninkatu, 3, Turku, Finland
b Åbo Akademi University, Finland, Porthaninkatu, 3, Turku, Finland
c Tampere University of Technology, Finland, Tampere, Finland
d New Energy Technologies Group, Department of Applied Physics, Aalto University, Puumiehenkuja 2, Aalto, 15100, Finland
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)
Benidorm, Spain, 2018 May 28th - 31st
Organizers: Emilio Palomares and Rene Janssen
Poster, Jan-Henrik Smått, 118
Publication date: 21st February 2018

The novel perovskite solar cell (PSC) technology is expected to soon outshine the conventional silicon-based solar cell technology as its record efficiency to date is already reaching over 22% [1]. However, before the PSC technology can break into the market, issues related to the poor reproducibility of the currently used processing methods have to be solved. Dip coating is a scalable and low-cost method for preparing uniform films with tunable thickness and structure, and we have previously utilized it for studying various charge selective layers in organic solar cells [2].

Recently, we utilized dip coating to improve the quality and to better understand the charge extraction mechanism in compact TiO2 layers in mesoscopic PSCs [3]. We chose TiCl4 as the sol-gel precursor, as we earlier demonstrated it gave rise to superior device properties [4]. By varying the TiCl4 concentration, we prepared ultra-thin (5−50 nm) compact TiO2 layers on FTO substrates. AFM measurements revealed that the thinnest TiO2 layers followed the texture of the underlying FTO substrates, while at thicknesses larger than ~25 nm the surface roughness substantially decreased. Furthermore, below this critical film thickness, the underlying FTO was partly exposed creating pinholes in the compact TiO2 layer.

Based on the performance of these layers in mesoscopic PSCs, a similar critical compact TiO2 layer thickness was identified. Devices without or with very thin compact TiO2 layers displayed poor efficiencies and J-V curves with an “s-shaped” feature in the negative voltage regime. This could be attributed to immobilized negative ions at the electron-extracting interface. A strong correlation between the magnitude of the s-shape feature and the exposed FTO indicated that the s-shape was related to the extent of pinholes in the compact TiO2 layer. The results highlight the importance of a uniform and pinhole-free electron selective TiO2 layer in efficient perovskite solar cells.

[1] https://www.nrel.gov/pv/assets/images/efficiency-chart.png

[2] O.J. Sandberg, S. Sandén, A. Sundqvist, J.H. Smått and R. Österbacka, Phys. Rev. Lett., 118, 076601 (2017).

[3] M.T. Masood, C. Weinberger, J. Sarfraz, E. Rosqvist, S. Sandén, O.J. Sandberg, P. Vivo, G. Hashmi, P.D. Lund, R. Österbacka and J.H. Smått, ACS Appl. Mater. Interfaces, ACS Appl. Mater. Interfaces, 9, 17906 (2017).

[4] P. Vivo, A. Ojanperä, J.H. Smått, S. Sandén, S.G. Hashmi, K. Kaunisto, P. Ihalainen, M.T. Masood, R. Österbacka, P.D. Lund and H. Lemmetyinen, Org. Electron., 41, 287 (2017).

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