Efficient Inverted Solar Cells Using Benzotriazole-Based Small Molecule and Polymers.

We synthesized medium-band-gap donor-acceptor (D-A) -type conjugated polymers (PBTZCZ-L and PBTZCZ-H) consisting of a benzotriazole building block as an acceptor and a carbazole unit as a donor. In comparison with the polymers, a small conjugated molecule (BTZCZ-2) was developed, and its structural, thermal, optical, and photovoltaic properties were investigated. The power conversion efficiency (PCE) of the BTZCZ-2-based solar cell devices was less than 0.5%, considerably lower than those of polymer-based devices with conventional device structures. However, inverted solar cell devices configured with glass/ITO/ZnO:PEIE/BTZCZ-2:PCBM/MoO/Ag showed a tremendously improved efficiency (PCE: 5.05%, : 9.95 mA/cm, : 0.89 V, and FF: 57.0%). We believe that this is attributed to high energy transfer and excellent film morphologies.