Self-assembled Poly(4-vinylpyridine) As an Interfacial Layer for Polymer Solar Cells

A nonconjugated polymer, poly(4-vinylpyridine) (PVPy), is applied to polymer solar cells (PSCs) as an interfacial layer (IFL) either inverted or conventional type PSCs. The Kelvin probe microscopy measurements support the formation of favorable interface dipole at the cathode interface, indicating the reduction of an electron collection barrier from the active layer to the cathode. Inverted type PSC with PVPy as an IFL demonstrate the power conversion efficiency (PCE) of 3.20%, (open circuit voltage [V-oc] = 0.61 V, short circuit current [J(sc)] = 8.68 mA/cm(2), fill factor [FF] = 59.4%), which is better than the device without interlayer (PCE = 2.95%, V-oc = 0.60 V, J(sc) = 8.11 mA/cm(2), FF = 60.6%). Most increase in the PCE of the devices with interlayer is resulted from enhancement of the Jsc. This is due to that the reduction of an electron collection barrier at the cathode interface. Conventional type PSC with PVPy (3.51%) at the cathode interface also exhibits better the PCE compared to that of the device without interlayer (2.88%).