Structural health monitoring (SHM) uses a network of sensors to be instrumented at critical locations in aerospace structures for timely damage detection. Some advanced technologies have been suggested for delamination detection of fiber-reinforced polymer (FRP) composites. However, these advanced sensors still suffer from dependency on an external power source. In particular, for cases where a large network of sensors is instrumented, power consumption by the sensor network may overwhelm the entire aerospace structural systems. To overcome the issue due to energy dependency of the state-of-the-art sensor technologies, self-powered sensors are needed for delamination detection in FRP of aerospace structures. In this study, a direct current (DC)-based strain sensor is suggested using multifunctional mechanoluminescent-optoelectronic (MLO) composites to be used for detection of delamination in FRP. First, an MLO-based strain sensor is fabricated using two functional materials: mechano-luminescent (ML) copper-doped zinc sulfide (ZnS:Cu)-based elastomeric composites and mechano-optoelectronic (MO) poly(3-hexylthiophene) (P3HT)-based thin films. Second, the sensor is then subjected to uniaxial sinusoidal cyclic loadings in a load frame and tested by varying strains and a constant loading rate to validate its DC-based strain sensing capability. DC responses are recorded during the cyclic loadings. Last, delamination detection in FRP is validated using the MLO sensor that is placed on an FRP test coupon, where pre-crack is formed to initiate delamination. The MLO-FRP specimen is subjected to cyclic loadings using 3-point bending test setup with varying maximum strains. The DC generated from MLO sensor is measured and compared to parameters calculated for assessing severity of delamination.