Solution-processed bulk heterojunction

Both phthalocyanines and squaraines are good candidates for bulk heterojunction solar cells. Recently, a supramolecular hetero-array of these functional dyes Pc-Sq-Pc (compound 52) has been reported for the first time, which exhibits a large coverage of the solar spectrum from 250 to 850 nm [51]. This axially held assembly serves as a robust panchromatic sensitizer. Upon excitation, it forms the radical ion pair Pc+-Sq -Pc with a long lifetime of 24 2 p,s. The use of this assembly as a donor material in solution processable bulk heterojunction solar cells has also been briefly studied. 

B. Walker, C. Kim, T.-Q. Nguyen, Small molecule solution-processed bulk heterojunction solar cells. Chem. Mater. 23, 470 (2010)... 

Characterization of the morphology of solution-processed bulk heterojunction organic photovoltaics ... 

Yamamoto T, Hatano J, Nakagawa T et al (2013) Small molecule solution-processed bulk heterojunction solar cells with inverted structure using porphyrin donor. Appl Phys Lett 102(1) 013305... 

Ma CQ, Fonrodona M, Schikora MC, Wienk MM, Janssen RAJ, Bauerle P (2008) Solution-processed bulk-heterojunction solar cells based on monodisperse dendritic oligothiophenes. Adv Fund Mater 18 3323-3331... 

Walker B, Kim C, Nguyen T-Q (2010) Small molecule solution-processed bulk heterojunction solar cellsf. Chem Mater 23 470... 

A series of ruthenium(II) phthalocyanines with one or two pyridyl dendritic olig-othiophene axial substituent(s) have also been reported (compounds 50 and 51) [50], The dendritic ligands absorb in the region from 380 to 550 nm, which complements the absorptions of the phthalocyanine core. This combination results in better light harvesting property and enhancement in efficiency of the corresponding solar cells. The solution-processed photovoltaic devices made with these compounds and fullerene acceptor give efficiencies of up to 1.6%. These represent the most efficient phthalocyanine-based bulk heterojunction solar cells reported so far. 

Figure 7.10 Tandem solar cell structure for polymer blend solar cells, based on the design demonstrated by Hadipour et al. (2006). In this all-solution-processed device, the top cell consists of a polymer PCBM bulk heterojunction with an absorption maximum of 550 nm and preferentially absorbs short-wavelength light, while the bottom cell is made from a bulk heterojunction of PCBM with a red-absortring polymer and absorbs longer-wavelength light. The composite gold-PEDOT PSS internal layer connects the two cells in...

Q. Sun, L. Dai, X. Xiaoli, L. Li, Q. Li, Bilayer- and bulk-heterojunction solar cells using liquid crystalline porphyrins as donors by solution processing. Appl. Phys. Lett. 91, 253505... 

K. M. Noone, E. Strein, N. C. Anderson, P.-T. Wu, S. A. Jenekhe, D. S. Ginger, Broadband Absorbing Bulk Heterojunction Photovoltaics Using Low-Bandgap Solution-Processed Quantum Dots. Nano Letters 2010, 10, 2635-2639. 

Janssen and coworkers have synthesized solution-processable conjugated oligomeric materials (221-222) combining electron-rich 2,5-dithienyl-N-dodecylpyrrole and electron-deficient 2,1,3-ben-zothiadiazole units. Bandgap of 1.60 and 1.46 eV was measured for thin films of 221 and 222, respectively. Bulk heterojunction realized with 221 and PCBM gave an efficiency of 0.34% [415]. 

Soa, S. Koa, FI. M. Kima, C. Paeka, S. Choa, N. Songb, K. Leec, J. K. Koa, J. Novel unsymmetrical push-pull squaraine chromophores for solution processed small molecule bulk heterojunction solar cells. Sol. Energ. Mat Sol. C., 2012,98,224-232. 

X 10 cm (V s ) at Vds= 30 V. These mobilities are the highest balanced mobilities reported so far for solution processed all polymer bulk heterojunction bipolar FETs. The balanced FET mobilities indicate the presence of sufficient percolation pathways for both charge carriers in these polymer blends. 

Small molecular materials for bulk heterojunction solar cells have attracted more and more attention during the last few years.There is a review chapter covering design of small molecular electron donor materials for bulk heterojunction solar cells.The power conversion efficiencies of the best solution-processible small molecular bulk heterojunction solar cells exceed 4-5% at present. ... 

Figure 65 Light-on I-V curves obtained for organic bulk heterojunction solar cells based on the PCPDTBT/[70]PCBM blends processed from chlorobenzene solutions with various additives. (Reprodueed from Ref. 183. American Chemical Society, 2008.)...

Matsuo Y, Sato Y, Niinomi T, Soga I, Tanaka H, Nakamura E (2009) Columnar structure in bulk heterojunction in solution-processable three-layered p-i-n organic photovoltaic devices using tetrabenzoporphyrin precursor and silylmethyl[60]fullerene. J Am Chem Soc 131 16048-16050. doi 10.1021/ja9048702... 

Huang Y, Li L, Peng X et al (2012) Solution processed small molecule bulk heterojunction organic photovoltaics based on a conjugated donor-acceptor porphyrin. J Mater Chem 22(41) 21841-21844... 

However, only small changes have a pronounced impact on the morphology of bulk heterojunction thin films as well as their charge carrier separation and transportation. This in turn influences the photovoltaic properties of the small molecule-based bulk heterojunction devices. Solution-processed organic solar cells based on the molecules with the shortest methyl end groups exhibit a high short circuit current and fill factor (128). 

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