Display omitted •PTB7-Th:PDIC5 films modified with chlronaphthalene were applied in OPVs.•Optical changes were monitored through ellipsometry spectroscopy.•n and k were used to simulate the spatial distribution of the electric field.•Exciton generation rate along the film thickness was reported.•Increased maximum current density with chloronaphtalene due morphological changes. In this work, a perylene derivative was used as electron acceptor in organic solar cells and the morphology was optimized by using the 1-chlronaphthalene (CN) as additive. The power dissipation was simulated along the structure of OPV devices taking into count the interference occurring in stacked thin films under normal incidence by using the transfer matrix method (TMM). The TMM model has been used to simulate the electric field in organic solar cells having fullerene derivatives as electron acceptor. In opposite to the fullerenes, the perylene derivative also contributes to the photocurrent and, its optical and electrical features changed upon CN additive. Therefore, the monitoring through ellipsometry and TMM modelling contribute to understand the behaviour of the electromagnetic wave inside the device, providing insights about proper optimizations that can be performed in order to increase the G(x) rate and the Jsc parameter. This model takes into count the experimental values of refractive index n and extinction coefficient k acquired from the D:A film to simulate the spatial distribution of the electric field and provide valuable information about photovoltaic parameters. The results pointed out that chemical or physical modifications are required to improve the PDIC5 acceptor distribution along the bulk, as well as changes on the crystallinity, which can be achieved with the use of CN as additive.