Phase behavior and morphological studies of active materials for small-molecule bulk heterojunction solar cells

• Main Authors: Chen, Ying-Cheng, 陳映誠
• Other Authors: Wang, Chien-Lung
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/70720712423713177319

碩士 === 國立交通大學 === 應用化學系分子科學碩博士班 === 101 === Optimized interpenetrating bicontinuous network made from a physcial blend of a p-type conjugated polymer and an n-type fullerene derivative is a prerequisite to achieve high power conversion efficiencies in bulk heterojunction (BHJ) organic solar cells (OSCs). According to Flory-Huggins theory, the physical state of a binary blend at constant pressure is governed by the free energy of mixing (Gmix). In this work, the phase behavior of a binary blend of two conjugated molecules BT(DTC6)2 and PC61BM was investigated through thermal analysis. The influence of processing temperature and blend ratio on Gmix was first determined. Interaction parameter (), entropy of mixing (Smix), and enthalpy of mixing (Hmix) were deduced based on the differential scanning calorimetry results. The binary blend of BT(DTC6)2/PC61BM has an interaction parameter ()= - 8*10-3 , which implies a negative Hmix and its Smix is positive. Thus the Gmix of the binary blend BT(DTC6)2/PC61BM is negative and the mixing phases of the two components should be spontaneous. In DSC study, we also find that crystalline temperature (Tc) of the components in the blend system relys on the blend ratio and resulted in a eutectic phase diagram. POM and TEM studies indicate the crystalline domain of BT(DTC6)2 decreases as the PC61BM ratio increases. Thermal and solvent annealing were further used to control the morphology of BT(DTC6)2/PC61BM. From atomic force microscope (AFM) and grazing-incidence small-angle X-ray scattering (GI-SAXS), we prove that we successful induce the crystallinity of BT(DTC6)2:PC61BM. It may indicate that while applying these methods to active layers of solar cells, we can accordingly optimize the electron donor and electron acceptor interface and sustain its crystallinity.