Showing papers by "Sean E. Shaheen published in 2006"
TL;DR: Inverted organic photovoltaic devices based on a blend of poly(3-hexylthiophene) and a fullerene have been developed by inserting a solution-processed ZnO interlayer between the indium tin oxide (ITO) electrode and the active layer using Ag as a hole-collecting back contact as discussed by the authors.
Abstract: Inverted organic photovoltaic devices based on a blend of poly(3-hexylthiophene) and a fullerene have been developed by inserting a solution-processed ZnO interlayer between the indium tin oxide (ITO) electrode and the active layer using Ag as a hole-collecting back contact. Efficient electron extraction through the ZnO and hole extraction through the Ag, with minimal loss in open-circuit potential, is observed with a certified power conversion efficiency of 2.58%. The inverted architecture removes the need for the use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as an ITO modifier and for the use of a low-work-function metal as the back contact in the device.
814 citations
TL;DR: In this article, the authors investigated the development of nanostructured oxide/conjugated polymer composite photovoltaic (PV) devices, which can take advantage of the high electron mobilities attainable in oxide semiconductors and can be fabricated using lowtemperature solution-based growth techniques.
521 citations
TL;DR: In this paper, the authors reported two viable organic excitonic solar cell structures where the conventional In2O3:Sn (ITO) hole-collecting electrode was replaced by a thin single-walled carbon nanotube layer.
Abstract: We report two viable organic excitonic solar cell structures where the conventional In2O3:Sn (ITO) hole-collecting electrode was replaced by a thin single-walled carbon nanotube layer. The first structure includes poly(3,4-ethylenedioxythiophene) (PEDOT) and gave a nonoptimized device efficiency of 1.5%. The second did not use PEDOT as a hole selective contact and had an efficiency of 0.47%. The strong rectifying behavior of the device shows that nanotubes are selective for holes and are not efficient recombination sites. The reported excitonic solar cell, produced without ITO and PEDOT, is an important step towards a fully printable solar cell.
382 citations
TL;DR: Study on pure films of P3HT demonstrate that charge carrier generation is an intrinsic feature of the polymer that occurs on the time scale of the excitation light, and this is attributed to the dissociation of bound polaron pairs that reside on adjacent polymer chains due to interchain charge transfer.
Abstract: We report on the ultrafast photoinduced charge separation processes in varying compositions of poly(3-hexylthiophene) (P3HT) blended with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Through the use of time-resolved terahertz spectroscopy, the time- and frequency-dependent complex photoconductivity is measured for samples with PCBM weight fractions (WPCBM) of 0, 0.2, 0.5, and 0.8. By analysis of the frequency-dependent complex conductivity, both the charge carrier yield and the average charge carrier mobility have been determined analytically and indicate a short (<0.2 nm) carrier mean free path and a suppressed long-range transport that is characteristic of carrier localization. Studies on pure films of P3HT demonstrate that charge carrier generation is an intrinsic feature of the polymer that occurs on the time scale of the excitation light, and this is attributed to the dissociation of bound polaron pairs that reside on adjacent polymer chains due to interchain charge transf...
147 citations
TL;DR: In this article, a bulk heterojunction organic photovoltaic device was fabricated by blending phenyl-cored thiophene dendrimers with a fullerene derivative.
Abstract: Bulk heterojunction organic photovoltaic devices have been fabricated by blending phenyl-cored thiophene dendrimers with a fullerene derivative. A power conversion efficiency of 1.3% under simulated AM1.5 illumination is obtained for a four-arm dendrimer, despite its large optical band gap of 2.1eV. The devices exhibit an increase in short-circuit current and power conversion efficiency as the length of the arm is increased. The fill factors of the devices studied are characteristically low, which is attributed to overly uniform mixing of the blend.
127 citations
TL;DR: This work demonstrates that care must be taken when using carboxylic acid side groups to attach polymers to titania surfaces in photovoltaic cells, if the density of attachment groups is just enough to attach the polymer, then the benefits of the interface modifier can be realized without substantially decreasing the open-circuit voltage.
Abstract: The interface of planar TiO2/polymer photovoltaic cells was modified with two carboxylated polythiophenes having different densities of carboxylic acid groups. Both of the interface modifiers increase the photocurrent of the cells but lower the open-circuit voltage. The work function of the TiO2, measured using a Kelvin probe, increases with increasing density of carboxylic acid groups due to the formation of interfacial dipoles pointing toward the TiO2 surface. The formation of interfacial dipoles results in a shift in the band offset at the TiO2/polymer interface, which explains the decrease in the open-circuit voltage. This work demonstrates that care must be taken when using carboxylic acid side groups to attach polymers to titania surfaces in photovoltaic cells. If the density of attachment groups is just enough to attach the polymer, then the benefits of the interface modifier can be realized without substantially decreasing the open-circuit voltage.
99 citations
Proceedings Article•
01 May 2006
TL;DR: In this paper, an organic solar cell with efficiencies of up to 1.43% and 2.6% using no ITO and no PEDOT:PSS was demonstrated.
Abstract: The conclusions of this report are that: (1) organic solar cells with efficiencies of up to 1.43% conversion efficiency that use no ITO and no PEDOT:PSS, are demonstrated; (2) a cell without ITO, but with PEDOT:PSS gave 2.6% conversion efficiency; (3) due to porous nature of SWCNT substrates, optimization of the active layer is essential; and (4) SWCNT electrodes bring one step closer the goal of a fully printable, organic solar cell.
01 May 2006
TL;DR: In this article, the authors reported two organic excitonic solar cell structures with the conventional ITO anode replaced by a thin single-walled carbon nanotube (SWCNT) layer.
Abstract: We report two organic excitonic solar cell structures with the conventional ITO anode replaced by a thin single-walled carbon nanotube (SWCNT) layer. The first structure, SWCNT/PEDOT/P3HT: PCBM/Al, gave a non-optimized device efficiency of 2.61%, which is competitive with ITO-based devices. The second, SWCNT/P3HT:PCBM/Al, is unique, as it did not use PEDOT as a hole selective contact. This had a promising efficiency of 1.43%. The open structure of the SWCNT network, and its inherent compatibility with the chlorobenzene solvent used to deposit the P3HT:PCBM, allow for intimate intermixing with the active layers of the device and the elimination of PEDOT. The strong rectifying behavior of the device shows that nanotubes are selective for holes and are not recombination sites in the active layer of the device. This excitonic solar cell is the first measurably efficient organic device produced without ITO and PEDOT.