High-efficiency standard and inverted polymer solar cells based on PBDTTT-C:[70]PCBM blend

The architecture of a polymer solar cell plays a crucial role on its stability because some of the materials used to build the device can suffer from degradation when exposed to air and/or oxygen. In this work we made a comparative study between the standard and the inverted polymer solar cells based on the bulk-heterojunction structure. We realized standard and inverted polymer solar cells using a blend film of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b´]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl] / [6,6]-phenyl C₇₁ butyric acid methyl ester (PBDTTT-C:[70]PCBM) blend films. In the standard architecture, the transparent indium tin oxide (ITO) electrode is coated with poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) and used as a hole collecting electrode, while in an inverted device configuration, the ITO electrode is turned into the electron collecting contact by surface modification with zinc oxide (ZnO). The standard cells sequence is ITO/PEDOT:PSS/PBDTTT-C:[70]PCBM/Ca/Al and the inverted cells one is ITO/ZnO/PBDTTT-C:[70]PCBM/MoO₃/Ag. We studied the electrical behavior (by means of IV-dark and IV-light at different illumination levels and external quantum efficiency measurements) of both kinds of devices in order to investigate the influence of the architecture (standard vs inverted) on the performance of the solar cells.