Humidity dependence of electrical performance of p-channel organic thin-film transistors ͑OTFTs͒ with various semiconductor compounds has been investigated. All devices showed decreased current output and mobility as the relative humidity ͑RH͒ was increased. The moisture sensitivity of the OTFT saturation current depends on the device geometry ͑bottom or top contact device͒ and channel length. The OTFT configuration with a short channel length and bottom contact was most affected by humidity compared to the top contact and larger channel length OTFT structures. The degradation of electrical performance under high RH is attributed to charge trapping at grain boundaries by polar water molecules reducing the rate of charge transport.

A conducting diblock copolymer of PS-b-P3HT was added to serve as a compatibilizer in a P3HT/PCBM blend, which improved the power-conversion efficiency from 3.3% to 4.1% due to the enhanced crystallinity, morphology, interface interaction, and depth profile of PCBM.

Various cyclohexyl end-capped oligomeric semiconductors based on oligothiophene, oligothiophene-fluorene, and perylene diimide have been synthesized using Stille and Suzuki coupling. These materials exhibit increased solubility over their unsubstituted and hexyl-substituted counterparts and have been successfully employed as the active component in organic field-effect transistors. The morphology of vacuum-deposited films made with these oligomers has been investigated using atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Field effect mobility as high as 0.17 cm2/V·s was observed in fluorene-thiophene oligomers deposited at elevated substrate temperatures. With the series of materials, a correlation between the size of the endgroup with respect to the size of the inner semiconducting core of the molecule is found to be an important factor in orienting the molecules with their long axis perpendicular to the substrate surface in the thin film phase, and directly related to charge transport in these materials.