Properties and mechanisms of iodine doped of P3HT and P3HT/PCBM composites

Polymeric conjugated materials are very promising for developing future soft material based semiconductors, conductors, electronic and optoelectronic devices due to their inherent advantages such as lightweight, flexible shape, low-cost, ease of processability, ease of scalability, etc. Like their inorganic counterparts, the addition of certain minority molecules or dopants can significantly alter the electronic and optoelectronic properties of the host conjugated polymers or composites allowing tunablilty for a variety of electronic/optoelectronic applications. In this report, P3HT and P3HT: PCBM doped with various iodine concentrations or doping levels were systematically examined for potential electronic/optoelectronic properties. This study finds that a 5% mole ratio iodine doping resulting in a smallest P3HT inter-layer gap of about 6.5 nm in the P3HT edge-on main chain packing style as well as smallest exciton bandwidth and most intense or ordered H-style aggregates, which may account for an optimal electronic/optoelectronic performance of the 5% doped P3HT/PCBM device. The results and findings could be useful to understand and to guide the design and development of future generation high efficiency molecular or polymer based optoelectronic devices, including solar cells and photodetectors.