Analytical modeling of bulk heterojunction organic solar cells incorporating spatial distribution of photocarrier generation

Abstract

This thesis presents an optoelectronic analytical model for bulk heterojunction organic solar cells. Incorporating optical transfer matrix theory in the electrical transport equations, we combine optical and electrical phenomena. This leads us to a single unified expression of current-voltage characteristic which considers the position and wavelength dependent carrier generation rate. Spatial distribution of the carrier generation rate is considered rigorously unlike previous analytical models. The model is capable of considering the optical propagation through the device structure as well as the optical phenomena such as reflections and interference effects. We verify the model with numerical results and published experimental data. We find that the consideration of spatial distribution of photocarrier generation rate is important to predict the device performance accurately. In addition, an analytical model for bulk heterojunction organic solar cells is developed on the basis of empirical expression of carrier generation rate. By developing the empirical formula and incorporating in the carrier transport equations, we successfully bring in the spatial distribution effect of generation rate into the current-voltage (J-V) characteristic of this solar cell. The proposed empirical formula helps us to derive the J-V curve expression, especially for the cases where carrier generation rate cannot be described by any physics-based closed form expression, and the spatial distribution of the generation rate profile to be extracted and used directly from published/available data. We justify our model by comparing with numerical simulations and published data. We observe that this model is capable of considering position dependency of carrier generation rate in a very simple and straightforward way.