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Remarkable advances have been seen in the area of organic photovoltaics (OPVs), with the power conversion efficiencies (PCEs) doubling in the past four year and exceeding over 18%. The commercial potential of OPV technology has been demonstrated, partly due to the fast development of new electron accepting materials. Although fullerene derivatives possess excellent electron mobility and affinity, they have some intrinsic limitations, including weak absorption in the visible region, elevated synthetic difficulty in tuning the electronic/optical properties, and poor morphology stability. Developing new electron acceptors to further improve the performance (including efficiency and stability) of OPV cells is necessary. This thesis focuses on the synthesis and charsterisation of novel electron accepting materials. Initially star-shaped oligomers were developed, however precise modulation of the molecular structure was needed to achieve proper energetics and high electron mobility. The unfavorable morphology, blended with electron donating materials, appeared to be another reason that limited the device performance. By combination of a benzodithiophene core and four diketopyrrolopyrrole arms, an oligomer was developed, which exhibited better p-type (electron donating) behavior in both OPV and organic field-effect transistor devices. Perylene diimide tetramers were developed to construct new electron acceptors and the broad absorption spectrum shown in ring-fused molecule was first explained by time-dependent density function theory (TD-DFT) calculations. In addition, linear ladder-type molecules were explored. Via a facile aromatic extension strategy, cyclopentadithienothiophene was prepared as a bent small molecule acceptor, which demonstrated promising device performance with high short-circuit current. Fully alkylated dithienocyclopentacarbazole flanked by electronwithdrawing nonfluorinated or fluorinated 1,1-dicyanomethylene-3-indanone were developed to investigate the effect of side chains and fluorination. Compared to the electron acceptor with bulky arylalkyl chains, alkyl side chains were found to enhance molecular packing and crystallinity and fluorination led to a more optimal nanoscale blend morphology and high performance. Finally, two wide-bandgap acceptors were developed for front-cell materials in tandem solar cells. High PCEs were achieved and in excellent agreement with theoretical simulations.