Organic photovoltaics (OPVs)
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Fig 1: Organic photovoltaic devices fabricated onto a flexible plastic substrate (photo by Lucy Pickford). |
Fig 2: An array of 36 organic photovoltaic devices forming the basis of a simple, low-resolution imaging device. |
Organic semiconductors are currently the subject of intense interest for their application in photovoltaic devices (solar cells). At Sheffield, we have a detailed research programme into organic photovoltaics based on thin-film blends of conjugated polymers and fullerenes (so-called bulk-heterojunction devices). When light is absorbed by the semiconducting polymer, an excited state can be formed termed an exciton. This state can be separated into an electron-hole pair by transferring an electron to the fullerene. By applying an electric field across the active film, the electrons and holes can be extracted, forming a photocurrent. This idea forms the basis of a photovoltaic device - see schematic in Figure 3 (below). We are currently exploring a range of different new electron donor polymers along with fullerene acceptors for application in photovoltaic devices - a selection of these are also shown in Figure 3. Here, our interest is both to understand the mechanisms that affect device efficiency and also develop manufacturable techniques to fabricate efficient devices.
Figure 3 above: Photovoltaic device schematic, with the chemical structures of a range of electron-donor polymers and fullerene acceptors.
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