The possibility of using an organic layer for controlling surface potential was investigated. The organic layer was formed by immersion in quinhydrone/methanol (QM) solution at room temperature. Surface passivation effects were estimated by lifetime measurements using the microwave photoconductive decay (m-PCD) method, and the surface condition was estimated by attenuated-total-reflection Fourier transform infrared (ATR-FTIR) measurement. Surface passivation effects due to the organic layer were clearly demonstrated. An increase in the lifetime of the wafer under illumination was observed. Charge trappings at the organic layer/silicon interface and in the organic layer were important for reducing surface recombination velocity. The organic layer can be formed at low temperature, and the formation process is simple. Hence, the application of an organic layer to silicon solar cells is expected for surface passivation films.