Effect of Fabrication Parameters on Three-Dimensional Nanostructures of Bulk Heterojunctions Imaged by High-Resolution Scanning ToF-SIMS
mediaposted on 2010-02-23, 00:00 authored by Bang-Ying Yu, Wei-Chun Lin, Wei-Ben Wang, Shin-ichi Iida, Sun-Zen Chen, Chia-Yi Liu, Che-Hung Kuo, Szu-Hsian Lee, Wei-Lun Kao, Guo-Ji Yen, Yun-Wen You, Chi-Ping Liu, Jwo-Huei Jou, Jing-Jong Shyue
Solution processable fullerene and copolymer bulk heterojunctions are widely used as the active layers of solar cells. In this work, scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to examine the distribution of [6,6]phenyl-C61-butyric acid methyl ester (PCBM) and regio-regular poly(3-hexylthiophene) (rrP3HT) that forms the bulk heterojunction. The planar phase separation of P3HT:PCBM is observed by ToF-SIMS imaging. The depth profile of the fragment distribution that reflects the molecular distribution is achieved by low energy Cs+ ion sputtering. The depth profile clearly shows a vertical phase separation of P3HT:PCBM before annealing, and hence, the inverted device architecture is beneficial. After annealing, the phase segregation is suppressed, and the device efficiency is dramatically enhanced with a normal device structure. The 3D image is obtained by stacking the 2D ToF-SIMS images acquired at different sputtering times, and 50 nm features are clearly differentiated. The whole imaging process requires less than 2 h, making it both rapid and versatile.