Open circuit voltage of organic solar cells: an in-depth review

Abstract

Organic solar cells (OSCs) have developed progressively in efficiency over the last two decades. Though it is promising, this technology is still far from realizing its full prospect. One of the most important parameters that determine the efficiency of OSCs is the open-circuit voltage (V_OC), which represents the maximum voltage a solar cell can provide to an external circuit. Light harvesting materials employed in OSCs have an optical band gap of around 1.7 to 2.1 eV and yet the V_OC barely exceeds 1.0 V, which is approximately just half of the photon's original energy. By contrast, in inorganic counterparts such as Si, CIGS and GaAs, the difference is only 0.3 to 0.45 eV between the material bandgap and V_OC. Hence, to achieve higher power conversion efficiencies (PCEs) in OSCs, a detailed understanding of the origins of V_OC and the associated energetic loss mechanisms is indispensable. The presented review takes the opportunity to elaborate various governing mechanisms and factors affecting the V_OC from a comprehensive yet insightful standpoint. This report also provides a concise synthesis of intricate interdependencies among the factors influencing V_OC and highlights the potential research strategies to improve V_OC, rendering possible pathways to facilitate the viable commercialization of OSCs.