Temperature/time-dependent crystallization of polythiophene:fullerene bulk heterojunction films for polymer solar cells

Abstract

We report the temperature/time-dependent crystallization of poly(3-hexylthiophene) (P3HT) in blend films of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC₆₁BM). The crystallization behaviour of P3HT:PC₆₁BM blend films was measured as a function of annealing time at two different temperatures (150°C and 160°C) by employing a synchrotron-radiation grazing-incidence angle X-ray diffraction (GIXD) technique. The crystallization behaviour was correlated with corresponding solar cells annealed under the same conditions. Results showed that the trend of device performance was almost in accordance with that of the (100) GIXD intensity, indicating that the nanostructure change in blend films does affect the device performance. However, the intermediate zones related to nanomorphology fluctuations, which were observed for lower temperature (140°C) annealing, were significantly suppressed at higher temperature (150°C and 160°C) annealing.

Morphological Characterization of a Low‐Bandgap Crystalline Polymer:PCBM Bulk Heterojunction Solar Cells

“…The most‐studied donor‐acceptor combination for polymer solar cells is a blend of poly(3‐hexylthiophene) (P3HT) and [6,6]phenyl‐C 61 ‐butyric acid methyl ester (PCBM), solution cast from 1,2‐dichlorobenzene ( o ‐DCB), where subsequent thermal annealing at temperatures well below the melting point of P3HT significantly improves device performance 7. The improved performance has been attributed to an improvement in the molecular ordering of P3HT within nanoscopic domains in the active layer,8, 9 enhanced separation of the components leading to phase purity, and preferential segregation of components to the anode and cathode interfaces 10. Scanning probe microscopy (SPM) techniques, including scanning force and Kelvin‐force microscopies,11–13 near‐edge X‐ray absorption fine structure analysis (NEXAFS)10, 14, 15 have been used to study the surface structure and morphology of the active layer.…”

“…Scanning probe microscopy (SPM) techniques, including scanning force and Kelvin‐force microscopies,11–13 near‐edge X‐ray absorption fine structure analysis (NEXAFS)10, 14, 15 have been used to study the surface structure and morphology of the active layer. Synchrotron‐based hard X‐ray techniques, including grazing incidence X‐ray diffraction (GIXD),8, 9, 16–19 grazing incidence small angle X‐ray scattering,20 resonance soft X‐ray scattering (RSoXS),21 NEXAFS analysis,10, 14, 15 and scanning transmission X‐ray spectromicroscopy22 have been used to characterize the ordering, orientation and phase behavior of the components near the surface and within the interior of the active layer.…”

Brush Polymer of Donor-Accepter Dyads via Adduct Formation between Lewis Base Polymer Donor and All Carbon Lewis Acid Acceptor

“…Overall, according to the above DSC data, the attachment of the bulky C 60 either as the end group in the case of dyads, or linked to the main chain/side chain junction point in the case of brush polymer, appeared to have some minor impact on the crystallization behavior of the P3HT units. Moreover, all XRD profiles ( Figure 17 ) of P3HT-(CH 2 ) 3 -VIM-C 60 and brush polymer adduct P[P3HT-(CH 2 ) 3 -VIM-C 60 ] showed a sharp peak at 5.30° to 5.53°, which is associated with the (100) reflection of P3HT [ 48 , 49 , 50 , 51 ]. In addition, intense peaks at 10.7° to 10.9°, as well as those appeared at 20.66° and 23.1°, associated with the adduct formation, were also observed.…”

Improved Performance of Polymer:Polymer Solar Cells by Doping Electron‐Accepting Polymers with an Organosulfonic Acid

“…To investigate the nanostructure change, we measured the diffraction patterns of blend films, mainly focusing on the P3HT crystals in the blend films 9, 20, 21. As shown in the 2D grazing‐incidence X‐ray diffraction (GIXD) images ( Figure a), the diffraction spot of the P3HT (100) planes in the out‐of‐plane (OOP) direction became more intense as the EBSA content increased, which is clearly observed from the 1D diffraction profiles (Figure 10b).…”

“…Introducing newly synthesized conjugated polymers has led to the further improvement of short‐circuit current density ( J SC ) and open‐circuit voltage ( V OC ) 12–14. Here, if we consider the fullerene nanocrystals embedded (or mixed) in the polymer films of polymer:fullerene solar cells, the morphological stability of the polymer:fullerene films can be problematic for the applications of flexible and/or bendable solar cell modules because the fullerene components are weakly bound to the polymer components, as proven by annealing studies 20–22…”