Influence of light absorption profile on the performance of organic photovoltaic cell using analytical drift diffusion model

Abstract

Organic photovoltaic (OPV) cell has several attractive features such as lightweight, good transparency, mechanical flexibility, and low production cost. However, their efficiencies are still relatively low to make OPV cell to be economically viable. A new approach on how to improve the efficiency of OPV cell is therefore necessary. In this thesis, how variation of light absorption at a specific position inside the active layer affects the performance of organic photovoltaic (OPV) cell, namely the short-circuit current density ( ), open-circuit voltage ( ), fill factor (FF), and power conversion efficiency (PCE), is investigated. To analyze the performance, a modified analytical current-voltage model for OPV cell is applied. The updated version allows the light absorption profile to be represented by any mathematical functions (e.g. an exponential function). It is found that light absorption profile affects the performance through the drift current. When the ratio of the mobility of the faster carrier to the mobility of the slower carrier type is less than 103, the PCE is maximized when the light absorption is concentrated at the center of the active layer (8.37%). When the ratio of the mobility of the faster carrier to the mobility of the slower carrier type is more than approximately 104, the PCE is maximized when the light absorption is concentrated near the electrode (6.65%). Therefore, the light absorption profile in an OPV cell needs to be properly tuned and adjusted in order to maximize the performance of the OPV cell.