Polymeric conjugated materials and composites are very promising for developing future soft material semiconductor and conductor based devices due to their inherent advantages such as lightweight, flexible shape, low-cost, ease of processability, ease of scalability, biocompatibility, etc. Like inorganic semiconductors, the addition of certain minority molecules or dopants can significantly alter the electronic structures and properties of the host conjugated polymers or composites allowing tunablilty for a variety potential applications including, but may not limited to, electronic devices (e.g., field effect transistors and related sensors), optoelectronic devices (e.g., photo sensors, solar cells), thermoelectric devices (e.g., temperature sensors, thermoelectric generators), etc. In this work, P3HT and P3HT:PCBM doped with various iodine doping levels were systematically evaluated on morphology, electronic property, and potential multi-function or sensor applications. This study finds that an optimal ratio of iodine doping resulting in a smallest inter-layer gap of the P3HT edge-on main chain packing style. This result may account for an optimal electronic/optoelectronic performance of an iodine doped P3HT/PCBM photoelectric device. Most importantly, the iodine/P3HT/PCBM ternary composite materials exhibit photoelectric and thermoelectric dual conversions simultaneously, and that one input can modulate the other conversion or function. The results and findings of this study could be very useful to understand and to guide the design and development of future generation high efficiency molecular or polymer based multifunction sensory or modulation devices.