Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L31: Organic Photovoltaic and Electrochromic Devices |
Hide Abstracts |
Sponsoring Units: DPOLY FIAP Chair: Graciela Blanchet, Dupont Room: LACC 503 |
Tuesday, March 22, 2005 2:30PM - 3:06PM |
L31.00001: Organic Semiconductor Photovoltaics Invited Speaker: Recent developments on organic photovoltaic elements are reviewed. Semiconducting conjugated polymers and molecules as well as nanocrystalline inorganic semiconductors are used in composite thin films. The photophysics of such photoactive devices is based on the photoinduced charge transfer from donor type semiconducting molecules onto acceptor type molecules such as Buckminsterfullerene, C$_{60}$ and/or nanoparticles. Similar to the first steps in natural photosynthesis, this photoinduced electron transfer leads to a number of potentially interesting applications which include sensitization of the photoconductivity and photovoltaic phenomena. Examples of photovoltaic architectures are discussed with their potential in terrestrial solar energy conversion. Several materials are introduced and discussed for their photovoltaic activities. Furthermore, nanomorphology has been investigated with AFM, SEM and TEM. The morphology/property relationship for a given photoactive system is found to be a major effect. [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:18PM |
L31.00002: Numerical Simulations of Layered and Blended Organic Photovoltaic Cells Sue Carter, Jan Haerter, John Scott We present results obtained from numerical simulations of organic photovaltaic cells as the donor-acceptor morphology evolves from sharply defined layers, to partial blends and finally homogeneous blends. We have employed a simple model that describes exciton dissociation and charge transport in continuously changing material concentrations. As the mixing percentage increases, the exciton dissociation increases and the diffusion counter-current decreases, resulting in substantially greater short circuit currents but reduced open circuit voltages. Blended structures are more sensitive to mobility than layers due to recombination throughout the bulk. Our model indicates that solar power efficiencies greater than 10\% can be achieved when the zero-field charge mobilities approach $10^{-3}$ cm$^2$/Vs for partially blended structures. [Preview Abstract] |
Tuesday, March 22, 2005 3:18PM - 3:30PM |
L31.00003: Efficiency of Organic Conjugated Polymer/C$_{60}$ Bulk Heterojunction Photovoltaic Devices D.B. Romero, M. Breban, C. Zhang, W.N. Herman We investigate the influence of thin-film morphology on the efficiency of organic conjugated polymer/C$_{60}$ bulk heterojunction polymer photovoltaic devices. Blends of soluble derivatives of fullerenes (PCBM- C$_{60}$) as electron acceptors and MEH-PPV or [MEH-PPV]-biphenylene-vinylene copolymer as donors are used in the fabrication the ITO/PEDOT:PSS/Polymer Blend/LiF/Al photocells. Thermal annealing effects on the phase segregation within the active layer are probed by scanning electron and atomic force microscopies. The micro/nano-structure morphologies are systematically correlated with the electrical and optical properties of the devices by current-voltage, capacitance- voltage, photocurrent, and electroabsorption spectroscopies. The implications of these results on the optimization of the open-circuit voltage, short-circuit current, and efficiency of the polymer photovoltaic devices will be explored. [Preview Abstract] |
Tuesday, March 22, 2005 3:30PM - 3:42PM |
L31.00004: High Efficiency Regio-Regular-P3HT/PCBM Flexible Solar Cells Kanzan Inoue, Pallavi Madakasira, Ross Ulbricht, Miaoxin Zhou, Xiaomei Jiang, Sergey Lee, John Ferraris, Anvar Zakhidov Solar cells (SCs) employing freshly synthesized home-made regio-regular poly(3-hexylthiophene) (RR-P3HT) and PCBM yielded nearly two fold increase of short circuit current, compared with the devices consisting of commercial RR-P3HT. The filling factor (FF) on the other hand decreased significantly resulting in the overall efficiency of 4{\%} for the device with commercial PHT from ADS. However, improving the serial resistance of the device can lead to much higher efficiency. The ideal homogenization of P3HT/PCBM solution and the optimal device heat-treatment [1] were used with the fresh home-made polymer to achieve the good phase separation of PCBM and RR-P3HT into a bi-continuous network structure. The best concentration of PCBM was found rather low; only 54 wt{\%} with respect to RR-P3HT in Toluene contrary to reported high 400 wt{\%} to PPV in 1,2 Dichlorobenzene. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L31.00005: Time-resolved Photoluminescence Studies of Various Polymer Heterojunction Films for Photovoltaics Stephanie V. Chasteen, Garry Rumbles, H.-H. Hoerhold, H. Tillman, Sue A. Carter Polymer photovoltaics provide a promising avenue for low-cost photovoltaics and other optoelectronics devices, but they are plagued by poor efficiencies. Photogenerated excitons (bound electron-hole pairs) must be separated in order to extract that charge as current. The exciton diffusion range is very short (about 20nm), leading to high recombination. Because excitons may be separated at a junction between an electron- and hole-accepting material, a reliable method of increasing device efficiencies is to create blended or layered heterojunction structures with mixing on the order of 20nm We create blended and layered heterostructures of a hole-transporting polymer (M3EH-PPV) with a variety of canonical electron-transporting materials: an electron-transporting polymer (CN-ether-PPV); PCBM; ITO; and TiO2 solgel and nanoparticles. Using time resolved photoluminescence, we are able to search for new excited state species as well as charge and energy transfer pathways which compete efficiently with charge recombination. Along with traditional device characterization, we thus achieve a rich understanding of how different electron-transporting materials affect exciton dynamics and recombination and thus device performance. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L31.00006: Temperature dependence of polymer hybrid solar cells Yuko Nakazawa, Sue Carter This presentation focuses on understanding the temperature dependent behaviors of polymer hybrid photovoltaic (PV) devices. The PV devices in this study consisted of a thin layer of PPV- based semiconducting polymer (M3EH-PPV) sandwiched between PEDOT and Al. Device architectures were modified by blending electron accepting CN- ether-PPV or PCBM in the photoactive layer, and evaporating LiF prior to Al (bulk heterojunction cells). Comparison will also be made between bulk and interfacial heterojunction structures, which consisted an additional layer of n-type semiconductor. Current-voltage characteristics were measured in a temperature- controlled cryostat to study the temperature dependence of PV parameters. Short circuit current (I$_{sc})$ and open circuit voltage (V$_{oc})$ were measured between 150 K and 400 K. The results showed Isc were more strongly affected by mobility in bulk heterojunction cells than in interfacial heterojunction structures. V$_{oc}$(T) were predominantly determined by device architecture than the mobility. Difference in underlying mechanism for polymer hybrid solar cells will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L31.00007: Photoconductivity of Hybrid Organic/Inorganic Quantum Dot Composite Xiaomei Jiang, Willam M. Sampson, Sergey Lee, Kanzan Inoue, Anvar Zakhidov We report the study of photoconductivity of hybrid organic/inorganic quantum dot composite in sandwich geometry. The uniform films of hybrid composite have been fabricated using conjugated polymers: either regio-regular poly (3-hexyl thiophene) or MEH-PPV and infrared PbSe quantum dots (QD) from Evident Technology Inc. We have observed the significant photoluminescence quenching (more than 30 times when excited by 400nm light) in MEH-PPV/QD composite with increasing concentration of quantum dots, photoluminescence spectrum profile shows obvious change with variation of excitation energy, with enhanced UV part luminescence as excitation moves to the blue side. Comparing with pure MEH-PPV, the main photoluminescence peak shows red-shift (up to 15nm). The enhanced photoresponse of sandwich device in comparison with pure polymer has been observed in broad spectral range from UV to NIR. The results demonstrate the efficient photoinduced charge transfer between polymer and QD and lead to possibilities of application of the polymer/IR QD in hybrid solar cells and photodetectors. [Preview Abstract] |
Tuesday, March 22, 2005 4:18PM - 4:30PM |
L31.00008: Solid State Electrochromic Devices Based on PPV Polymers Amanda Holt, Janelle Leger, Sue Carter We present a solid state electrochromic device structure employing a PPV-based light-emitting polymer more commonly used in devices such as LED's and photovoltaics. We explore device performance as a function of salt type, salt concentration and polymer layer thickness. These devices display high reversibility, dramatic optical contrasts, and low operating voltages comparable to state of the art conducting polymer electrochromic devices. We found that salts employing organic anions display slightly improved optical contrasts. Also, thicker devices, higher voltages and higher salt concentrations produce higher optical contrasts at the cost of slowed switching speeds. Apart from novel electrochromic applications these devices also provide insight into the fundamental process of doping in PPV-based polymer solid-state devices, crucial knowledge for the development of applications of polymer light emitting electrochemical cells (LECs), actuators and sensors. We explore the dependence of PL efficiency on doping level and discuss possible implications for the doping of PPV polymers in a solid state device configuration. [Preview Abstract] |
Tuesday, March 22, 2005 4:30PM - 4:42PM |
L31.00009: In-situ spectroscopic investigation of infrared transmissive/absorptive electrochromic devices. Maria Nikolou, David B. Tanner, Zhuangchun Wu, Andrew G. Rinzler, Aubrey L. Dyer, Timothy Steckler, John R. Reynolds Novel transmissive/absorptive electrochromic (EC) devices have been assembled using conjugated polymers on infrared-transparent electrodes made of single-wall carbon nanotubes (SWNTs). We will present results on the design, fabrication and characterization of sandwich type EC devices using dioxythiophene-based conjugated polymers (PXDOT). The polymers were prepared on the SWNT films using a potentiostatic electropolymerization method. The transmittance of the samples was measured over the infrared through visible energy range. To extract the optical constants of the polymer, we modeled all layers of this multilayer thin film structure using a Drude-Lorentz model. From the parameters obtained, we compute optical constants which yield information about the electronic structure of the neutral and doped states of the polymer. Evidence for polaron states at low doping and bipolaron states at maximum doping will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 4:42PM - 4:54PM |
L31.00010: Solid-state electrochromic device for 8-12 $\mu $m based on Poly(3,4-ethylenedioxythiophene) Ilsup Jin, Bruce Dunn Poly(3,4-ethylenedioxythiophene) (or PEDOT) was used as the electrochromic element for solid-state devices operating in the 8-12 $\mu $m range. The reflection-mode devices used anti-reflection coated germanium windows as the substrate in order to minimize surface reflection and increase the contrast ratio of the device. Upon doping the polymer using a gel electrolyte, there was a substantial change in the refractive index of PEDOT which induced a large index mismatch with the substrate and produced high reflection from the substrate/PEDOT interface. The reflection modulation between the doped and undoped states was approximated using Fresnel's equation and estimates of the refractive index mismatch. The calculated values were in reasonable agreement with the experimental results. When PEDOT was fully doped, the device exhibited its maximum reflection of 50-60{\%} in the 8- 12 $\mu $m regime, while in the undoped state, the device had 10-20{\%} reflection. The maximum contrast ratio observed for the device, $\sim $ 5.5, occurred at 8.25 $\mu $m. The use of rapid scans of the FT-IR enabled us to monitor, in real time, the infrared switching dynamics. Switching times on the order of 1 to 2 seconds were observed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700