Organic photovoltaic cells with controlled polarization sensitivity

Abstract

In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of %6.1 and %1.6 were achieved, respectively. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4868041] Organic photovoltaics (OPVs) have attracted significant research interest due to several advantageous characteristics, including low-cost processing onto flexible substrates, tunable properties through material synthesis, and their use of earth abundant materials. 1 A unique characteristic of polymer semiconductors is that they commonly have an optical transition dipole moment (p À p*) that is aligned along the polymer backbone. 2,3 Thus, aligning the polymer backbone uniaxially in the plane of the film results in anisotropic optoelectronic properties. 4-6 Aligning polymer semiconductors has been exploited to study charge transport in organic field effect transistors (OFETs) 4,7 and for polarized electroluminescence in organic light emitting diodes. 8 Alignment also provides an opportunity to develop polarization sensitive OPV devices. 6,9 Polarization sensitive photovoltaic cells may be beneficial for a number of applications including polarized light detectors (e.g., remote detection), 10 and power generation (e.g., polarized light harvesting in LCD displays). 6 In addition, alignment of the polymer chains in an OPV cell may provide insight into energy conversion processes. 11 There have been a number of techniques used to uniaxially align conjugated polymer films that have focused on alignment of homogeneous polymer systems. 4,7,[12][13][14] In polymer:fullerene blends, such as poly(3-hexylthiophene): Phenyl-C61-butyric acid methyl ester (P3HT:PCBM), alignment of the P3HT component has recently been demonstrated by (1) mechanically rubbing the film at an elevated temperature (150 C) 6 and (2) through directed crystallization. 15 While the directed crystallization approach was successful, it required processing with a crystallizing solvent 1,3,5-trichlorobenzene (TCB) and OPV devices using this approach have yet to be produced. 15 Furthermore, while the mechanical rubbing approach effectively aligns P3HT in P3HT:PCBM blend films, the physically interrogating rubbing process at an elevated temperature may be detrimental to the film's quality. Additionally, the ability to control the degree of alignment with this approach is unclear. In this study, we demonstrate a facile approa...

Intrinsic coincident linear polarimetry using stacked organic photovoltaics

“…The magnitude of the responsivity anisotropy has previously been shown to increase with the magnitude of the applied strain due to the increasing alignment of the polymer backbones [17,20]. A detailed analysis of the polarized OPV cell performance has shown that the internal quantum efficiency of the device remains similar to an unstrained device and is independent of the incident polarization state [24].…”

“…This property has been exploited to fabricate polarization sensitive organic photovoltaic (OPV) devices [17,21], which consist of polymer-fullerene bulk-heterojunction (BHJ) active layers. In the demonstration by Awartani et al [17], the polarization sensitivity was achieved by employing a strain-alignment approach that allows for fine control of the level of polymer alignment and thus the magnitude of the polarization response. Applying uniaxial strain to the P3HT:PCBM [poly(3hexylthiophene):Phenyl-C61-butryc acid methyl ester] active layer, plastically deforms the film and the polymer backbones align to the direction of strain, resulting in a long-range oriented polymer film.…”

“…The strain aligned P3HT:PCBM photoactive layer is then transfer printed onto the PEIE layer. This process has been previously described in detail [17]. The film is then thermally annealed at 135 °C for 10 minutes.…”

“…The polarimeter is based on semitransparent, strain-aligned polymer semiconductor-based organic photovoltaics (OPVs). Unlike previous intrinsically polarization sensitive detectors [15,16] our approach implements semitransparent devices by exploiting oriented polymer semiconductor films [17,18]. Through this semi-transparency, the issue of instantaneous and spatially-coincident spatial sampling is resolved in a device that has the potential of becoming monolithic.…”

Synthesis and Characterization of Conducting Copolymers PANi‐PTh for Photovoltaic Cell Applications

“…[1] The OPV device fabrication methods, bulk-heterojunction the photoactive layer has been extensively studied. [2] Organic photovoltaics (OPV) solar cells are currently the most investigated architectures, allowing the preparation of large area devices using simple and effective techniques, i.e. roll-toroll, [3] ink-jet [4] and doctor blading processing, [5] leading to current certified efficiencies up to 10%.…”