We review infrared and Raman analyses of thin films of organic semiconductors used for active layers in organic solar cells. We present Raman study of blend (bulk heterojunction) films of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The contents of the crystalline region of P3HT in the blend films prepared by various methods were estimated by Raman spectroscopy. Temperature dependence of photoinduced infrared absorption from a P3HT:PCBM blend film gives the activation energy of the recombination of photoinduced positive and negative carriers. The activation energies for P3HT:PCBM blend films with various PCBM contents were obtained. It has been demonstrated that infrared and Raman spectroscopy is useful for evaluating thin films of P3HT:PCBM blend films used for organic solar cells.