Self-assembled poly(4-vinylpyridine) as an interfacial layer for polymer solar cells : PVPy SAM as an interfacial layer

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\ua0oc] = 0.61 V, short circuit current [J\ua0sc] = 8.68 mA/cm2, fill factor [FF] = 59.4%), which is better than the device without interlayer (PCE = 2.95%,\ua0V\ua0oc\ua0= 0.60 V,\ua0J\ua0sc\ua0= 8.11 mA/cm2, FF = 60.6%). Most increase in the PCE of the devices with interlayer is resulted from enhancement of the\ua0J\ua0sc. 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%)

A Simple Approach to Fabricate an Efficient Inverted Polymer Solar Cell with a Novel Small Molecular Electrolyte as the Cathode Buffer Layer

A novel small-molecule electrolyte, 1,1′-bis­(4-hydroxypropyl)-[4,4′-bipyridine]-1,1′-diium bromide (V-OH), containing a mixture of PTB7:PC₇₁BM has been designed and synthesized as a cathode buffer layer for inverted polymer solar cells (iPSCs). The molecular structure of this new compound comprises a viologen skeleton with hydroxyl group terminals. While the viologen unit is responsible for generating a favorable interface dipole, the two terminal hydroxyl groups of V-OH may generate a synergy effect in the magnitude of the interface dipole. Consequently, the devices containing the V-OH interlayer exhibited a power conversion efficiency (PCE) of 9.13% (short circuit current = 17.13 mA/cm², open circuit voltage = 0.75 V, fill factor = 71.1%). The PCE of the devices with V-OH exhibited better long-term stability compared to that of the devices without V-OH. Thus, we found that it is possible to enhance the efficiency of PSCs by a simple approach without the need for complicated methods of device fabrication