Flexible, conjugated polymer-fullerene-based bulk-heterojunction solar cells: Basics, encapsulation, and integration
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A. Labouret Solems, 91124 Palaiseau Cédex, France (Received 22 June 2005; accepted 8 August 2005)
Organic solar cells based on conjugated polymer:fullerene blends show nowadays efficiencies above 4%. After briefly presenting the science of bulk-heterojunction solar cells, we report herein a shelf lifetime study performed by encapsulating the cells in a flexible and transparent gas barrier material. This method allows lifetimes as reported for glass encapsulation. Moreover, we propose a new approach to pattern organic solar cells and design large-scale modules. This technique, based on selective Nd:yttrium aluminum garnet (YAG) laser etching, potentially enables low-cost, high-speed roll-to-roll operation.
I. INTRODUCTION
The worldwide photovoltaic (PV) industry reached a module production of 750 MWp in 2003 and has exhibited an annual growth of 30% over the last five years.1 Thus, PV appears as one of the most promising renewable energy sources. The same year, the PV sector represented an overall market of about US $5.8 billion. As shown in Fig. 1, this development is not only observed in Japan, but also in Europe, yet the United States has shown only limited interest. Besides, most Japanese, American, and European roadmaps seem to agree on one point: This tendency is expected to last at least for the next 30 years to come.1 A significant capacity of about 140 GWp is forecast to be operational around the globe in 2030. This number is the equivalent of 100 state-of-theart nuclear power plants. This worldwide enthusiasm for PV combined with a general interest for organic semiconductors explain why organic solar cells are the object of increasing attention. Since the first report of a molecular thin film solar cell,2 several concepts have been proposed using small molecules by vacuum evaporation,3 solution-processed conjugated polymer blends (“bulk heterojunctions”),4–6 and organic–inorganic material blends (“hybrid” solar cells).7,8 Those organic semiconductors open new opportunities for PV cell design due to their light weight,
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0399 3224
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 12, Dec 2005 Downloaded: 31 May 2014
mechanical flexibility, and semi-transparency. Among them, conjugated polymers appear especially promising due to their processing advantage:9 they can be made soluble in common organic solvents10 and hence deposited by simple solution processing and printing technologies. Thin films on flexible or inflexible substrates are achievable by well-known and widespread printing methods like screen,11 inkjet,12 offset, or flexo printing. Therefore, low-cost mass production by roll-to-roll process can be technologically envisaged. Nevertheless, to achieve a product viable in the market and competitive with other available technologies, polymer-based solar cells have to fulfill cost, efficiency, and lifetime13 requirements. Today, conjugated polymerbased photovoltaic devices have been reported
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