Third Generation Solar Cells: Semitransparent, Efficient & Low-Cost

An innovative use of graphene has helped researchers develop a semitransparent perovskite solar cell.

AsianScientist (Sep. 16, 2015) – Developing transparent or semitransparent solar cells with high efficiency and low cost to replace the existing opaque and expensive silicon-based solar panels has become increasingly important due to the increasing demands of the building integrated photovoltaics (BIPVs) systems.

Now, researchers at the Hong Kong Polytechnic University (PolyU) have successfully developed efficient and low-cost semitransparent perovskite solar cells with graphene electrodes. Their findings have been published in Advanced Materials.

The power conversion efficiencies (PCEs) of their semitransparent solar cells are around 12 percent illuminated by fluorine-doped tin oxide bottom electrodes (FTO) or graphene top electrodes. In contrast, conventional semitransparent solar cells achieve PCEs of about seven percent. At a potential cost of less than US$0.06/Watt, such solar cells are expected to be 50 percent cheaper than existing silicon solar cells.

First generation crystalline silicon solar panels are highly stable and have efficient energy conversion, but are opaque and expensive. The second generation solar cells, namely thin film solar cells, are lightweight and can be made flexible. However, they are made of rare materials with complicated structures and need high temperature treatments.

In recent years, scientists have been investigating third generation solar cells. Perovskite solar cell as a novel third generation solar cell has attracted much attention recently due to its high power conversion efficiency, convenient fabrication process and potentially low cost.

With the aim of improving PCEs and reducing costs of semitransparent solar panels, the researchers developed the first-ever made semitransparent perovskite solar cells with graphene as electrode. Graphene is an ideal candidate for transparent electrodes in solar cells with high transparency, good conductivity and potentially low cost.

The semitransparent feature of the solar cell enables it to absorb light from both sides, making it suitable for use in windows, facades, louvers and the rooftops of buildings, thus increasing the surface area for collecting solar energy substantially.

While graphene has been known for over a decade, the research team enhanced the conductivity of graphene to meet the requirement of its applications in solar cells.

Firstly, the conductivity of graphene was dramatically improved by a thin coating of conductive polymer poly-(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), that was also used as an adhesion layer to the perovskite active layer during the lamination process.

Secondly, to further improve the efficiency of power conversion, the researchers found that by fabricating the solar cell with multilayer chemical vapor deposition graphene as the top transparent electrodes, the sheet resistance of the electrode could be further reduced while maintaining the high transparency of the electrodes.

Lastly, the performance of the solar cell was further optimized by improving the contact between the top graphene electrodes and the hole transport layer (spiro-OMeTAD) on the perovskite films.

Because of the excellent mechanical flexibility of graphene and the simple preparation of the devices, the semitransparent perovskite solar cell can be used in mass production with printing or roll to roll process. The semitransparent solar cells are expected to fill the gap in the market, performing functions that existing solar cells are unable to.

The article can be found at: You et al. (2015) Efficient Semitransparent Perovskite Solar Cells with Graphene Electrodes.

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Source: The Hong Kong Polytechnic University.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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