Broadband transparent sputtered indium zinc oxide rear electrode for perovskite solar cells

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, Jérémie Werner, 076
Publication date: 5th February 2015

Owing to their wide band gap and high efficiency, perovskite solar cells are highly interesting candidates for high-efficiency tandem devices in combination with narrow-bandgap absorber materials such as crystalline silicon or chalcogenides. However, perovskite cells are usually opaque, typically with an evaporated metal rear electrode. Therefore, in order to use perovskite cells in a tandem configuration, the rear electrode has to be replaced by a material with a high transparency in the near-infrared spectral region. Several materials have already been tested as transparent rear electrodes on perovskite solar cells, including carbon nanotubes and silver nanowires. These materials however typically suffer from rather limited transparency in the infrared and/or require complicated processing methods with large sample-to-sample variation, limiting the throughput and the potential to up-scale these technologies. Here, we show that amorphous transparent conductive oxides are particularly attractive as transparent electrode for perovskite solar cells. Specifically, we use sputtered indium zinc oxide (IZO), which has a particularly high electron mobility when deposited at room temperature and low power and does not require post-deposition annealing. This can yield a low resistivity even when deposited onto the temperature-sensitive layers of perovskite solar cells. By inserting a thin metal-oxide buffer layer between the organic hole transport layer and the IZO rear electrode, we avoid sputter damage. This is confirmed by low-illumination current-voltage measurements, which show that any sputter damage related extraction barrier can be eliminated by the buffer layer. Using this optimized transparent rear electrode, we obtained perovskite cells with power conversion efficiencies over 10% for an active area of 0.25 cm², with good transparency in the red and near infrared, above 60% in the 800-1200 nm wavelength range. The IZO electrode that was employed for these cells absorbs less than 3% in the 400-1200 nm wavelength range at a sheet resistance of 30 Ohm/square. Moreover, it is fabricated with simple, up-scalable, and industrially-compatible deposition techniques. These results demonstrate that our transparent IZO rear electrode is highly suitable for tandem solar cell applications. We demonstrate the potential for high-efficiency photovoltaic devices by applying the developed semitransparent perovskite solar cell in a four-terminal tandem device with a silicon heterojunction bottom solar cell. In summary, we demonstrate the applicability of sputtered IZO as a transparent rear electrode for efficient perovskite solar cells with high near-infrared transparency, paving the road towards high-efficiency perovskite/c-Si tandem devices.

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