Excitons play a critical role in determining the optical and electrical properties of organic semiconductor devices. Two types of excitons, namely Frenkel and charge transfer excitons, are formed in these systems. The nature of the excitons is a deciding factor for the efficiency of radiative recombination or dissociation into free carriers. We used electroabsorption spectroscopy to investigate the nature of the excitons contributing to the various features of the absorption spectra in PPDT2FBT thin films. Analysis of the measured electroabsorption spectra indicated both Frenkel and charge transfer characteristics for the band edge states in PPDT2FBT. For various practical applications, blends of different organic semiconductors, acting as donor acceptor pairs, are used. Electroabsorption spectra of blended films of PPDT2FBT:PCBM of different blend compositions showed no new signatures compared to the EA spectrum of pristine PPDT2FBT. However, an increase in the charge transfer nature of the excitons and polarizability of the molecules was observed. Carrier collection efficiency from the bulk of the film was found to increase with PCBM concentration. Besides the role played by PCBM, the internal electric fields of the devices also influence the charge transport efficiencies. We estimated the internal fields in the active layer of organic semiconductor devices. The induced fields due to space charges were attributed to deep traps, which are otherwise difficult to probe by standard methods. The trapped carrier densities and trap state energies were estimated for P3HT and PPDT2FBT.