Fabrication of 4 terminal perovskite//CIGS tandem solar cell using optical splitting method
Akira Yamada a, Kazuyoshi Nakada a, Takahito Nishimura a, Tsutomu Miyasaka b, Youhei Numata b
a Tokyo Institute of Technology, 2-12-1 Oookayama, Meguro-ku, Tokyo, Japan
b Toin University of Yokohama, 1614 Kurogane-cho, Aoba, Yokohama, 2258503, Japan
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
Poster, Kazuyoshi Nakada, 009
Publication date: 7th November 2016

The potential of 4 terminal perovskite//CIGS tandem solar cell was evaluated by optical splitting method. In the 4 terminal approach, there is flexibility in cell design since the current matching required in 2 terminal device is not needed. Additionally, adjusting of the polarity of the top cell back electrode and bottom cell top electrode is not required. On the other hand, in the splitting method, the top and bottom cells can be evaluated on their original and already developed single junction structure, without any adaption such as application of transparent back electrode for the top cell used in stacked structures. The optical splitting method is realized by the use of an optical filter installed in an angle of 45 degrees between the light source and bottom cell. The optical filter used in this work was designed to reflect the light with wavelength shorter than 620 nm, and to transmit the longer wavelength light. The perovskite cell is set perpendicularly to the bottom cell to receive the light reflected by the optical filter.

The efficiencies of the perovskite and CIGS single solar cells used in this work under 1 sun condition were 13.3% (JSC 22.0 mA/cm2, VOC 1.03 V, FF 58.4%) and 18.8% (JSC 38.7 mA/cm2, VOC 0.651 V, FF 74.4%), respectively. The cell area and bandgap estimated from the absorption edge of the perovskite solar cell were 9 mm2 and 1.5 eV, respectively. Similarly, the area and estimated bandgap of the CIGS solar cell were 15 mm2 and 1.1 eV, respectively.

The efficiencies of the perovskite and CIGS solar cells after splitting were 9.0% (JSC 12.2 mA/cm2, VOC 1.03 V, FF 71.5%) and 12.1% (JSC 25.7 mA/cm2, VOC 0.637 V, FF 73.9%), respectively, resulting in a total efficiency of 21.1%. Interestingly, FF of the perovskite top cell improved after splitting, while VOC remains the same. This could be related to the lower injection condition under splitting. On the other hand, VOC of the CIGS bottom cell after splitting decreased according to the decrease in JSC, which in turn is close to the value estimated from EQE. Considering the bandgap of the solar cells used in this work, an optical filter with a cutting wavelength of 770 nm should result in a higher total efficiency. Further efficiency improvement is expected by using an optical filter with lower absorption loss and by the application of a top solar cell with a bandgap of 1.7–1.8 eV.

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