Efficient Organic Photovoltaics Utilizing Nanoscale Heterojunctions in Sequentially Deposited Polymer/fullerene Bilayer

A highly efficient sequentially deposited bilayer (SD-bilayer) of polymer/fullerene organic photovoltaic (OPV) device is developed via the solution process. Herein, we resolve two essential problems regarding the construction of an efficient SD-bilayer OPV. First, the solution process fabrication of the SD-bilayer is resolved by incorporating an ordering agent (OA) to the polymer solution, which improves the ordering of the polymer chain and prevents the bottom-layer from dissolving into the top-layer solution. Second, a non-planar heterojunction with a large surface area is formed by the incorporation of a heterojunction agent (HA) to the top-layer solution. Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole- 4,7-diyl-2,5-thiophenediyl] (PCDTBT) is used for the bottom-layer and phenyl-C71-butyric-acid-methyl ester (PC70BM) is used for the top-layer. The SD-bilayer OPV produced utilizing both an OA and HA exhibits a power conversion efficiency (PCE) of 7.12% with a high internal quantum efficiency (IQE). We believe our bilayer system affords a new way of forming OPVs distinct from bulk heterojunction (BHJ) systems and offers a chance to reconsider the polymers that have thus far shown unsatisfactory performance in BHJ systemsope

Crystallinity Effects in Sequentially Processed and Blend-Cast Bulk-Heterojunction Polymer/Fullerene Photovoltaics

Although most polymer/fullerene-based solar cells are cast from a blend of the components in solution, it is also possible to sequentially process the polymer and fullerene layers from quasi-orthogonal solvents. Sequential processing (SqP) not only produces photovoltaic devices with efficiencies comparable to the more traditional bulk heterojunction (BHJ) solar cells produced by blend casting (BC) but also offers the advantage that the polymer and fullerene layers can be optimized separately. In this paper, we explore the morphology produced when sequentially processing polymer/fullerene solar cells and compare it to the BC morphology. We find that increasing polymer regioregularity leads to the opposite effect in SqP and BC BHJ solar cells. We start by constructing a series of SqP and BC solar cells using different types of poly(3-hexylthiophene) (P3HT) that vary in regioregulary and polydispersity combined with [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM). We use grazing incidence wide-angle X-ray scattering to demonstrate how strongly changes in the P3HT and PCBM crystallinity upon thermal annealing of SqP and BC BHJ films depend on polymer regioregularity. For SqP devices, low regioregularity P3HT films that possess more amorphous regions allow for more PCBM crystallite growth and thus show better photovoltaic device efficiency. On the other hand, highly regioregular P3HT leads to a more favorable morphology and better device efficiency for BC BHJ films. Comparing the photovoltaic performance and structural characterization indicates that the mechanisms controlling morphology in the active layers are fundamentally different for BHJs formed via SqP and BC. Most importantly, we find that nanoscale morphology in both SqP and BC BHJs can be systematically controlled by tuning the amorphous fraction of polymer in the active layer. © 2014 American Chemical Society

Biofunctional silicon nanoparticles by means of thiol-ene click chemistry

The preparation and characterization of butylene-terminated silicon nanoparticles (SiNPs) and their functionalization using thiol-ene chemistry is described, as well as the coupling of DNA strands. Bromide-terminated SiNPs were prepared by means of the oxidation of magnesium silicide and functionalized with butylene chains through treatment with the corresponding Grignard reagent. The successful coupling was confirmed by NMR and FTIR spectroscopy. TEM measurements revealed a silicon-core diameter of (2.4±0.5) nm. The fluorescence emission maximum is at ¿max=525 nm when excited at ¿exc=430 nm. The conjugation of these alkene-terminated SiNPs by means of thiol-ene chemistry is described for a variety of functional thiols. Efficient coupling was evidenced by NMR and FTIR spectroscopy. Moreover, the characteristic fluorescence properties of the SiNPs remained unaltered, thus demonstrating the value of this approach towards functional oxide-free SiNPs. Activation of the attached carboxylic acid moieties allowed for conjugation of NH2-terminated oligo-ssDNA (ss=single strand) to the SiNPs. Successful coupling was confirmed by a characteristic new UV absorption band at 260 nm, and by the still-present distinctive fluorescence of the SiNPs at 525 nm. Gel electrophoresis confirmed coupling of 2 to 3 DNA strands onto the SiNPs, whereas no uncoupled DNA was observed

Biofunctional Silicon Nanoparticles by Means of Thiol-Ene Click Chemistry

The preparation and characterization of butylene-terminated silicon nanoparticles (SiNPs) and their functionalization using thiol-ene chemistry is described, as well as the coupling of DNA strands. Bromide-terminated SiNPs were prepared by means of the oxidation of magnesium silicide and functionalized with butylene chains through treatment with the corresponding Grignard reagent. The successful coupling was confirmed by NMR and FTIR spectroscopy. TEM measurements revealed a silicon-core diameter of (2.4±0.5) nm. The fluorescence emission maximum is at ¿max=525 nm when excited at ¿exc=430 nm. The conjugation of these alkene-terminated SiNPs by means of thiol-ene chemistry is described for a variety of functional thiols. Efficient coupling was evidenced by NMR and FTIR spectroscopy. Moreover, the characteristic fluorescence properties of the SiNPs remained unaltered, thus demonstrating the value of this approach towards functional oxide-free SiNPs. Activation of the attached carboxylic acid moieties allowed for conjugation of NH2-terminated oligo-ssDNA (ss=single strand) to the SiNPs. Successful coupling was confirmed by a characteristic new UV absorption band at 260 nm, and by the still-present distinctive fluorescence of the SiNPs at 525 nm. Gel electrophoresis confirmed coupling of 2 to 3 DNA strands onto the SiNPs, whereas no uncoupled DNA was observed

Correction to Preparation, Characterization, and Surface Modification of Trifluoroethyl Ester-Terminated Silicon Nanoparticles

P 4311. The author name Veronique S. Gevaerts was misspelled in the original paper

Influence of the Position of the Side Chain on Crystallization and Solar Cell Performance of DPP-Based Small Molecules

Three isomeric π-conjugated molecules basedon diketopyrrolopyrrole and bithiophene (DPP2T) substitutedwith hexyl side chains in different positions areinvestigated for use in solution-processed organic solar cells.Efficiencies greater than 3% are obtained when a mildannealing step is used. The position of the side chains onthe DDP2Ts has a major influence on the optical andelectronic properties of these molecules in thin semicrystallinefilms. By combining optical absorption and fluorescencespectroscopy, with microscopy (AFM and TEM) andscattering techniques (GIWAXS and electron diffraction), we find that the position of the side chains also affects themorphology and crystallization of these DPP2Ts when they are combined with a C70 fullerene derivative in a thin film. The studydemonstrates that changing the side chain position is an additional, yet complex, tool to influence behavior of conjugatedmolecules in organic solar cells.KEYWORDS: small molecules, solar cells, side chain engineering, morphology, crystallinit

A Universal Route to Fabricate n-i-p Multi-Junction Polymer Solar Cells via Solution Processing

The interconnection layer (ICL) that connects adjacent subcells electrically and optically in solution-processed multi-junction polymer solar cells must meet functional requirements in terms of work functions, conductivity, and transparency, but also be compatible with the multiple layer stack in terms of processing and deposition conditions. Using a combination of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, diluted in near azeotropic water/n-propanol dispersions as hole transport layer, and ZnO nanoparticles, dispersed in isoamyl alcohol as electron transport layer, a novel, versatile ICL has been developed for solution-processed tandem and triple-junction solar cells in an n-i-p architecture. The ICL has been incorporated in six different tandem cells and three different triple-junction solar cells, employing a range of different polymer-fullerene photoactive layers. The new ICL provided an essentially lossless contact in each case, without the need of adjusting the formulations or deposition conditions. The approach permitted realizing complex devices in good yields, providing a power conversion efficiency up to 10%

A universal route to fabricate n-i-p multi-junction polymer solar cells via solution processing

The interconnection layer (ICL) that connects adjacent subcells electrically and optically in solution‐processed multi‐junction polymer solar cells must meet functional requirements in terms of work functions, conductivity, and transparency, but also be compatible with the multiple layer stack in terms of processing and deposition conditions. Using a combination of poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate, diluted in near azeotropic water/n‐propanol dispersions as hole transport layer, and ZnO nanoparticles, dispersed in isoamyl alcohol as electron transport layer, a novel, versatile ICL has been developed for solution‐processed tandem and triple‐junction solar cells in an n‐i‐p architecture. The ICL has been incorporated in six different tandem cells and three different triple‐junction solar cells, employing a range of different polymer‐fullerene photoactive layers. The new ICL provided an essentially lossless contact in each case, without the need of adjusting the formulations or deposition conditions. The approach permitted realizing complex devices in good yields, providing a power conversion efficiency up to 10%