Wednesday, 17 Jul 2019

Researchers develop novel method to fabricate low-cost perovskite solar cells

In developing the method, the scientists realised that making the perovskite layer 1 micron thick increased the working life of the solar cell significantly

OIST - Dr. Zonghao Liu (left) and Prof. Yabing Qi (right) with the 5 cm × 5 cm perovskite solar module that they developed

28 Sep 2018 | Editor

Researchers from the Energy Materials and Surface Sciences Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) have reported that they believe they have found a winning formula in a new method to fabricate low-cost high-efficiency solar cells.

Prof. Yabing Qi and his team from OIST in collaboration with Prof. Shengzhong Liu from Shaanxi Normal University, China, developed the cells using the materials and compounds that mimic the crystalline structure of the naturally occurring mineral perovskite. Their technique has recently been published in Nature Communications.

According to Prof. Qi solar cell technologies need to fulfil three conditions - "the golden triangle" - to be worth commercialising:

  • their conversion rate of sunlight into electricity must be high
  • they must have a long lifespan
  • they must be inexpensive to produce

Today, most commercial solar cells are made from crystalline silicon, which has a relatively high efficiency of around 22%. Though silicon, the raw material for these solar cells, is abundant, processing it tends to be complex and increases manufacturing costs, making the finished product expensive.

Prof. Qi believes that perovskite offers a more affordable solution.

The researchers say perovskite was first used to make solar cells in 2009 by Prof. Tsutomu Miyasaka's research team at Toin University of Yokohama, Japan, and since then it has been rapidly gaining importance.

"Research on perovskite cells is very promising. In only nine years, the efficiency of these cells went from 3.8 % to 23.3%. Other technologies have taken over 30 years of research to reach the same level"

Prof. Yabing Qi, Energy Materials and Surface Sciences Unit at the Okinawa Institute of Science and Technology Graduate University (OIST)

The fabrication method he and his research team have developed produces perovskite solar cells with an efficiency comparable to crystalline silicon cells, but it is potentially much cheaper than making silicon solar cells.

To make the new cells, the researchers coated transparent conductive substrates with perovskite films that absorb sunlight very efficiently. They used a gas-solid reaction-based technique in which the substrate is first coated with a layer of hydrogen lead triiodide incorporated with a small amount of chlorine ions and methylamine gas – allowing them to reproducibly make large uniform panels, each consisting of multiple solar cells.

In developing the method, the scientists realised that making the perovskite layer 1 micron thick increased the working life of the solar cell significantly.

In addition, a thicker coating not only boosted the stability of the solar cells but also facilitated the fabrication processes, thereby lowering its production costs.

"The solar cells are almost unchanged after working for 800 hours"

"The thicker absorber layer ensures good reproducibility of solar cell fabrication, which is a key advantage for mass manufacturing in the realistic industrial-scale setting"

Dr. Zonghao Liu, Postdoctoral scholar in Prof. Qi's research group

The big challenge Prof. Qi and his team now face is in increasing the size of their newly designed solar cell from the 0.1 mm2 sized prototype to large commercial-sized panels that can be several feet long. This is where the industry can help.

"There exists a large gap between the findings in lab and reality, and the industry is not always ready to cover this entire gap by itself. So, the researchers need to take one more necessary step beyond their labs and meet the industry half-way."

Prof. Qi

To take that step, Prof. Qi and team received a generous grant from OIST's Technology Development and Innovation Center, under their Proof-of-Concept Program. With that funding, the team has built a working model of their new perovskite solar modules consisting of multiple solar cells on 5 cm × 5 cm substrates, with an active area of 12 cm2 - much bigger than their experimental prototype but smaller than what is required for commercial purposes.

Although the process of scaling-up has reduced the efficiency of the cells from 20% to 15%, the researchers are optimistic that they will be able to improve the way they work in the coming years and successfully commercialise their use.

Gas-solid reaction based over one-micrometer thick stable perovskite films for efficient solar cells and modules

Zonghao Liu | Longbin Qiu | Emilio J. Juarez-Perez | Zafer Hawash | Taehoon Kim | Yan Jiang | Zhifang Wu | Sonia R. Raga | Luis K. Ono | Shengzhong (Frank) Liu | Yabing Qi

Nature Communications volume 9 | Article number: 3880 (2018) | DOI: 10.1038/s41467-018-06317-8


Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to fabricate perovskite films with thickness over 1 μm in ambient condition on the basis of the fast gas−solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 ± 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cm × 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T80 lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.

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Source: Okinawa Institute of Science and Technology

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