Rubidium Multi-Cation Optimized-Bandgap Perovskite Cells for High Efficiency Perovskite/Silicon Tandems
The Duong a, Klaus Weber a, Kylie Catchpole a, Thomas White a
a Centre for Sustainable Energy Systems, Research School of Engineering, Australian National University, CECS, Bldg 32, North Road, Canberra, 2601
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Oral, The Duong, presentation 122
Publication date: 7th November 2016

Perovskite solar cells with their simple solution processed fabrication, high efficiency and tunable bandgap are very promising to combine with silicon solar cells in a tandem configuration. For this type of tandem, perovskite active material with a bandgap of 1.7 – 1.8 eV is optimal. However, it is challenging to achieve a good performance for perovskites in this bandgap range due to high energetic disorder and low charge carrier mobility. Combined with the stringent requirement for the semi-transparent perovskite top cell to have very low sub-bandgap absorption, this has limited the achievable perovskite/silicon tandem efficiency. Here we explore rubidium (Rb) as an alternative cation to use in a novel multi-cation method with the formamidinium (FA)/methylammonium (MA)/cesium (Cs) system to obtain 1.75 eV bangap perovskite cells with negligible hysteresis and steady state efficiency of more than 17%. Our study shows the beneficial effect of Rb in improving the crystallinity and suppressing defects in the perovskite material. In parallel, we developed a sputtered indium doped tin oxide thin film to be used as a transparent contact with absorption of less than 5% in the long wavelength region. Using these two developments, we fabricated semi-transparent perovskite cells with efficiency of up to 14.8% and average transparency of more than 80% (peak at ~84%) between 720 nm and 1100 nm. In a tandem configuration using a 23.9% silicon cell, we demonstrated 24.7% efficiency (9.9% from silicon cell) in a mechanically stacked tandem configuration. We identify a clear pathway to break the single junction silicon cell record of 26.33% in the future.

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