A new method to visualize the large-scale crystal grain morphology of organic polycrystalline films is proposed. First,optical anisotropic transmittance images of polycrystalline zinc phthalocyanine(Zn Pc) films vacuum deposited by weak epitaxial growth(WEG) method were acquired with polarized optical microscopy(POM). Then morphology properties including crystal grain size, distribution, relative orientation, and crystallinity were derived from these images by fitting with a transition dipole model. At last, atomic force microscopy(AFM) imaging was carried out to confirm the fitting and serve as absolute references. This method can be readily generalized to other organic polycrystalline films, thus providing an efficient way to access the large-scale morphologic properties of organic polycrystalline films, which may prove to be useful in industry as a film quality monitoring method.
In this paper,we investigated the recombination dynamics of photogenerated charge carriers in a poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C 61-butyric acid methyl ester(PC 61 BM) blend system with donor-acceptor ratio of 1:1 before and after solvent annealing treatment.The technique of transient photocurrent and photovoltage measurements were used,and charge carriers were photogenerated by a 7 ns laser pulse at room temperature(298 K).In transient photocurrent measurement,we observed some differences in the saturation extracted charge in P3HT:PCBM solar cells with different power efficiencies.In addition,the bimolecular recombination coefficient is found to be 3.5×10-13 cm 3 s-1 for annealed devices,while 9.5×10-12 cm3 s-1 for as-cast devices.In the transient photovoltage measurement,we found that the photovoltage decay can be fitted by power-law equation at long time scale.The exponent parameter is 2.6 for annealed devices,which can be described as trap-free bimolecular recombination;is 1.76 for as-cast device due to the trap-limited bimolecular recombination.These experimental results indicate that the nanomorphology of active layer indeed have influence on charge carriers dynamics in P3HT:PCBM blend systems.
