POSS-Enhanced Phase Separation in Air-Processed P3HT:PCBM Bulk Heterojunction Photovoltaic Systems

Abstract

Nanoparticles have been shown in some cases to improve phase separation and morphology in bulk heterojunction organic photovoltaic cells. In this study, the effect of incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules of different structures in air processed poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) films and photovoltaic cells was evaluated. Morphology and composition of the nanoscalephase-separated domains were determined via conductive atomic force microscopy in conjunction with nanomechanical mapping and Raman imaging. UV-vis and fluorescence spectroscopy analysis of the films was performed at different stages of the process and with different levels of solvent vapor and thermal annealing. It was found that POSS molecules of selected structures provided enhancement in morphology control in films, translating to improvements in fill factor and power conversion efficiency of laboratory-scale OPV cells. The findings indicate the potential for further improvements in solar cell performance with specifically tailored POSS/polymer phase-separated systems.

Air processed P3HT:PCBM photovoltaic cells: Morphology correlation to annealing, degradation, and recovery

“…In these images, the bright features (high DMT Modulus) are attributed to the PCBM phase, while dark areas are attributed to the low modulus P3HT phase. 7 The film prepared without annealing shows weak phase separation [ Fig. 7(A)], where P3HT and PCBM domains are dispersed on the surface and no ordered morphology is observed, as has been reported previously.…”

“…Photoactive blends prepared without annealing exhibit weak phase separation, but phase separation can be improved by applying annealing techniques, including thermal, solvent, and solvent vapor annealing (SVA). [5][6][7] Phase separation, however, is a thermodynamically meta-stable state in which phase separated domains tend to aggregate into larger domains over time. 8 When the domain size exceeds the exciton diffusion length, the performance decreases.…”

Pharmacological Modulators of Tau Aggregation and Spreading

“…As an early pathological event, progressive hyperphosphorylation leads to the dissociation of tau from microtubules, which apparently alters cytoskeleton dynamics and impairs axonal transport, resulting in synaptic dysfunction [67] ( Figure 1A). Soluble tau proteins undergo conformational changes that can be key drivers for aggregation to begin [68][69][70][71]. Progressive hyperphosphorylation and increased local tau concentrations in restricted areas promote misfolding and lead to neuropathological alterations in AD brains, particularly correlated with synaptic loss and tangle formation [72][73][74], accompanied by astrogliosis [75,76], and microglial cell activation [76][77][78].…”

Quantitative characterization of phase separation in the photoactive layer of polymer solar cells by the phase image of atomic force microscopy

“…To investigate the effect of morphology on the performance of PSCs, various techniques have been adopted to characterize the phase separation of active layer, such as atomic force microscopy (AFM) [23][24][25][26][27], transmission electron microscopy [26][27][28][29], grazing-incidence x-ray diffraction or scattering [25,[30][31][32], small-angle neutron scattering [17,32], and photoluminescence and Raman spectroscopy [2,33]. Among them, AFM is one of the most important tools to characterize the phase separation and has been widely used since the nanoscale morphology and domain formation of blend films can be directly observed by using the phase image of AFM.…”