Absorption, polymer solar cell

Hoppe H, Shokhovets S, Gobsch G (2007) Inverse relation between photocurrent and absorption layer thickness in polymer solar cells. Phys Status Solidi RRL 1 R40... 

Transparent polymer solar cells (i.e., polymer solar cells with transparent electrodes) can be easily fabricated based on inverted architecture and have important application in tandem architectures as well. We can form transparent solar cells by replacing the Al top electrode with 12 nm Au in the inverted structure. The J-V curves for this transparent polymer solar cell, with light incident from ITO and Au side, are shown in Figure 11.17. The difference between the two J-V curves is due to the partial loss by the reflection and absorption at the semitransparent Au electrode. To provide sufficient electrical conductance, Au layer thickness has to be sufficient and the optical loss at Au electrode becomes significant. However, the inverted solar cell structure has the V2O5 layer which is not only transparent but also provides effective protection to the polymer layer. A transparent conductive oxides electrode, such as ITO, can therefore be deposited without compromising device performance. 

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. 

Li, Y., 2012. Molecular design of photovoltaic materials for polymer solar cells toward suitable electronic energy levels and broad absorption. Acc. Chem. Res. 45, 723-733. 

J. W. Jung, F. Liu, T. P. Russell, W. H. Jo, Semi-crystalline Random Conjugated Copolymers with Panchromatic Absorption for Highly Efficient Polymer Solar Cells. Energy Environ. Sci. 2013, 6, 3301. 

Once we obtain the erternal quantum efficiency of polymer solar cells, the value of Jsc can be calculated from the overlap between the absorption spectra of the materials and the sunlight AM 1.5 G spectrum. 

I 72 Fullerene/Conjugated Polyiner Composite for the State-of-the-Art Polymer Solar Cells 12.3.1.1 Absorption Enhancement... 

X. Zhan, Z. Tan, B. Domercq, Z. An, X. Zhang, S. Barlow, Y. Li, D. Zhu, B. Kippelen and S. R. Marder, A high-mobility electron-transport polymer with broad absorption and its use in field-effect transistors and all-polymer solar cells, J. Am. Chem. Soc., 129, 7246-7247 (2007). 

Figure 16.6 Four physical processes in the power conversion of all-polymer solar cells photon absorption, exciton diffusion, dissociation of charge-transfer states, and charge-carrier transport and collection.

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