Thin polymer heterojunctions

A significant increase in the forward current and in the FF is observed for conjugated polymer/fullerene bulk heterojunction solar cells upon insertion of a thin layer of LiF between the organic layer and the Al electrode (negative electrode of the solar cell), as shown in Fig. 5.37a and b. 

Hoppe H, Arnold N, Meissner D, Sariciftci NS (2004) Modeling of optical absorption in conjugated polymer/fullerene bulk-heterojunction plastic solar cells. Thin Solid Eilms 451-452 589... 

The photophysics of jt-conjugated polymers are reviewed in detail in other chapters of this book. (See, for example, Chapter 3.) Here, we focus on the electronic and photophysical phenomena that occur at the heterojunction between two different semiconductor polymers. The heteroj unctions are formed by combining four different polyfluorene copolymers in blend or bilayer thin films and are investigated using time-resolved and steady-state, temperature- and elec-tric-field-dependent photoluminescence measurements as well as electroluminescence and time-resolved spectroscopy. We review a body of work carried out in our laboratories over the last few years, and published in numerous journal articles (see refs. [13-17]). 

At the early development of polymer solar cells, a planar p-n junction structure represented the mainstream in mimicking conventional silicon-based solar cells. However, the obtained devices demonstrated poor photovoltaic performances due to the long distance between the exciton and junction interface and insufficient light absorption due to the thin light absorber. It was not until 1995 that the dilemma was overcome with the discovery of a novel bulk heterojunction in which donor and acceptor form interpenetrated phases. Poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene] was blended with Ceo or its derivatives to form the bulk heterojunction. A much improved power conversion efficiency of 2.9% was thus achieved under the illumination of 20 mW/cm. (Yu et al., 1995). The emergence of the donor/acceptor bulk-heterojunction structure had boosted the photovoltaic performances of polymer solar cells. Currently, a maximal power conversion efficiency of 10.6% had been reported on the basis of synthesizing appropriate polymer materials and designing a tandem structure (You et al., 2013). The detailed discussions are provided in Chapter 5. 

The first solid-state dye-sensitized heterojunction of Ti02 and a semiconducting polymer was reported by Murakoshi and coworkers [19, 7]. They formed a solid-state heterojunction by photoelec-trochemical polymerization of pyrrole into a nanoporous Ti02 film, sensitized with Ru(dcbpy)2(SCN)2. Direct contact of polypyrrole and the FTO back contact was suppressed by electrodeposition of a thin Ti02 film before the adsorption of the dye onto the nanocrystalline Ti02 electrode. The doping density of the polymer was controlled electrochemically. Solar energy conversion efficiencies were somewhat... 

M.-H. Chen, J. Hou, Z. Hong, G. Yang, S. Sista, L.-M. Chen, Y. Yang, Efficient Polymer Solar Cells with Thin Active Layers Based on Alternating Polyfluorene Copolymer/Fullerene Bulk Heterojunctions. Adv. Mater. 2009, 21,4238-4242. 

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