The role of buffer layers in polymer solar cells

The present review rationalizes the information spread in the literature concerning the use and role of buffer layers in polymer solar cells. Usual device structures include buffer layers, both at the anode and at the cathode interface, mainly to favour charge collection and extraction, but also to improve the device's overall performance. Buffer layers are actually essential for achieving highly efficient polymer solar cells and can no more be considered as "optional", thus the need and importance of understanding their properties and role. The aim of this review is to give the reader an overview of this topic and to provide a practical and useful tool for the daily activities of researchers in the field of polymer photovoltaics.