Amorphous vs crystalline exciton blocking layers at the anode interface in planar and planar-mixed heterojunction organic solar cells

Abstract

We compare the gain in power conversion efficiency (PCE) achieved by inserting either amorphous or crystalline exciton blocking layers at the anode interface for planar (PHJ) and planar-mixed heterojunction (PM-HJ) organic solar cells based on Tetraphenyldibenzoperiflanthene and fullerenes. For PHJ devices, there is a gain of more than 37% for both types of blocking layers, mainly due to an increase in photocurrent, indicating that this gain can be solely ascribed to the exciton blocking effect. A templating effect as proposed in literature for crystalline blocking layers cannot be affirmed. On the contrary, it is shown that there is a connection between the choice of acceptor (C60/C70) and the blocking effect on the anode side. Moreover, we can show that also for PM-HJ devices a remarkable efficiency enhancement is possible. The insertion of suitable blocking layers at the anode interface can alter the effective work function and thus the open-circuit voltage, leading to a maximum PCE of 5.8% in single junction cells.