Low bandgap polymers, and

Figure 9.2 RSoXS of DPP based low bandgap polymer and PC71BM blends.

Zhou Y, Tvingstedt K, Zhang EL, Du CX, Ni WX, Andersson MR, Inganas O (2009) Observation of a charge transfer state in low-bandgap polymer/fullerene blend systems by photoluminescence and electroluminescence studies. Adv Funct Mater 19 3293... 

The use of low bandgap polymers (ER < 1.8 eV) to extend the spectral sensitivity of bulk heterojunction solar cells is a real solution to this problem. These polymers can either substitute one of the two components in the bulk hetero junction (if their transport properties match) or they can be mixed into the blend. Such a three-component layer, comprising semiconductors with different bandgaps in a single layer, can be visualized as a variation of a tandem cell in which only the current and not the voltage can be added up. 

Fig. 5.41. Schematic overview of different strategies for spectral sensitization of bulk heterojunction solar cells utilizing a low bandgap polymer, (a) shows the scenario for an energy transfer between the dye and the low bandgap polymer, while (b) illustrates the scenario for an electron transfer between the dye and the low bandgap polymer...

Wienk M. M., Struijk M. P. and Janssen R. A. J. (2006), Low bandgap polymer bulk heterojunction solar cells , Chem. Phys. Lett. 422, 488-491. 

J. Peet, J.Y. Kim, N.E. Coates, W.L. Ma, D. Moses, A.J. Heeger, and G.C. Bazan, Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nature Mater., 6, 497-500 (2007). 

R.-Y. Tian, R.-Q. Yang, Q.-M. Zhou, J.-B. Peng, and Y. Cao. Performances of photovoltaic cells based on Se-containing low-bandgap polymer. Hua-nan Ligong Daxue Xuebao, Ziran Kexueban (Journal of South China University of Technology), 33 6-9, 18,2005. 

For example, the effectiveness of low-bandgap polymers in absorbing more light has been demonstrated by comparing P3HT CdSe- and PCPDTBT CdSe-based devices [187]. It can be seen from Figure 3.26a that low-bandgap CP poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,l-b 3,4-b0] -dithiophene)-alt-4,7-(2,l, 3-benzothiadiazole)] (PCPDTBT)... 

Y. Zhou, M. Eck, C. Veit, B. Zimmermann, F. Rauscher, P. Niyamakom, S. Yilmaz, I. Dumsch, S. Allard, U. Scherf, Efficiency Enhancement for Bulk-Heterojunction Hybrid Solar Cells Based on Acid Treated CdSe Quantum Dots and Low Bandgap Polymer PCPDTBT. Solar Energy Materials and Solar Cells 2011,95,1232-1237. 

J. Seo, M. J. Cho, D. Lee, A. N. Cartwright, P. N. Prasad, Efficient Heterojunction Photovoltaic Cell Utilizing Nanocomposites of Lead Sulfide Nanocrystals and a Low-Bandgap Polymer. Advanced Materials 2011, 23, 3984-3988. 

Y. Zhou, et al. Efficiency enhancement for bulk-heterojunction hybrid solar cells based on acid treated CdSe quantum dots and low bandgap polymer PCPDTBT. Solar Energy Materials Solar Cells, 2011.95(4) p. 1232-1237. 

L. Dou, et al.. Systematic investigation of benzodithiophene- and diketopyr-rolopyrrole-based low-bandgap polymers designed for single junction and tandem polymer solar cells. Journal of the American Chemical Society, 2012. 134(24) p. 10071-10079. 

The synthesis of the tellurophene-containing low-bandgap polymer PDPPTe2T by microwave-assisted, palladium-catalyzed, ipso-arylative polymerization of 2,5-bis[(a,a-diphenyl)methyl]tellurophene in the presence of diketopyrrolopyrrole (DPP) monomer was reported (14AG(1)10691). This is the first PV device prepared from a tellurophene polymer. IPCE measurements showed that substitution from sulfur to tellurium causes a red shift in absorption and enables donor materials to collect up to 1 pm. 

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