Electron spin resonance (ESR) study was performed on organic layered films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/pentacene that were fabricated with different deposition speed of pentacene on PEDOT:PSS in order to investigate charge formation at the PEDOT:PSS/pentacene interfaces. Clear increases in ESR signals of not only pentacene but also PEDOT were observed, which are caused by the charge transfer at the interfaces. The charge transfer is prominent at high deposition speed of pentacene, which means that slow deposition speed is suitable for solar-cell fabrication without charge formation.