Currently in use for a variety of applications, including optical communication, spectroscopy, imaging sensors, and biological sensors in the medical field, organic photo detectors belong to the class of organic semiconductors. At their junction, photo detectors typically transform optical signals that is, light or photons into electrical current. In this case, organic semiconductors are preferred over inorganic ones due to their low processing temperature, ease of fabrication, greater flexibility, and increased defect sensitivity. However, the dark current in these OPDs can rise in response to temperature, which leads to low temperature sensitivity. This in turn reduces the optoelectronic features of OPD such as the gain, detectivity, and responsivity. The purpose of this article is to explain how different types of nanostructure gratings, like moth eye nanostructures, can be added to organic photovoltaic (OPD) structures in order to increase their absorption level. This will allow us to achieve a higher signal to noise ratio, which will improve signal detection even in low intensity situations. The FDTD method was used to simulate OPDs. By adding moth eye nanostructures to OPDs, we can improve the electric field intensity and absorption. This will increase the generation rate of electron hole pairs, which will increase the efficiency of the OPD.