Hou-Chin Cha

Correlation between Hierarchical Structure and Processing Control of Large-area Spray-coated Polymer Solar Cells toward High Performance

The formation mechanism of a spray-coated film is different from that of a spin-coated film. This study employs grazing incidence small- and wide-angle X-ray Scattering (GISAXS and GIWAXS, respectively) quantitatively and systematically to investigate the hierarchical structure and phase-separated behavior of a spray-deposited blend film. The formation of PCBM clusters involves mutual interactions with both the P3HT crystal domains and droplet boundary. The processing control and the formed hierarchical structure of the active layer in the spray-coated polymer/fullerene blend film are compared to those in the spin-coated film. How the different post-treatments, such as thermal and solvent vapor annealing, tailor the hierarchical structure of the spray-coated films is quantitatively studied. Finally, the relationship between the processing control and tailored BHJ structures and the performance of polymer solar cell devices is established here, taking into account the evolution of the device area from 1 × 0.3 and 1 × 1 cm2. The formation and control of the special networks formed by the PCBM cluster and P3HT crystallites, respectively, are related to the droplet boundary. These structures are favorable for the transverse transport of electrons and holes.

Performance Improvement and Characterization of Spray-Coated Organic Photodetectors

Low dark current organic photodetectors (OPDs) with a conventional structure consisting of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as active layer have been fabricated by spray-coating. Tuning the thickness of active layer and thermal annealing process for the spray-coated OPDs results in a remarkable performance with a low dark current density ( Jd) of 2.90 × 10-8 A/cm2 at reverse bias of 1 V. The impact of thermal annealing on the performance of sprayed OPDs is also investigated by the impedance analysis for mechanistic understanding. Our results demonstrate that the optimization of PCBM cluster and interfacial contact between the active layer and the metal electrode tailored by thermal annealing, respectively, could effectively reduce the Jd and increase the sensitivity of sprayed OPDs. The control of PCBM cluster is more important than the interfacial contact between the layers for improving Jd. In addition, structural characterization of the active layer studied by synchrotron small-angle X-ray scattering technique reveals why the spray-coated process can achieve the lowest dark current due to the favorable structure.