Cathode modification of polymer solar cells by electrostatically self-assembled zwitterionic non-conjugated polyelectrolyte

• Zwitterionic polymer based on poly(4-vinylpyridine) (PVPy-ZW).
• Electrostatically self-assembled PVPy-ZW modifies the work function.
• PVPy-ZW enhances the efficiency of polymer solar cells.

A non-conjugated zwitterionic polylectrolyte (PVPy-ZW) based on poly(4-vinylpyridine) is applied to polymer solar cells (PSCs) as a cathode buffer layer either inverted or conventional type polymer solar cells. The Kelvin probe microscopy measurement support the formation of favorable interface dipole at the cathode interface, indicating the reduction of a Schottky barrier for an electron collection from the active layer to the cathode. Inverted type PSC with the PVPy-ZW as a cathode buffer layer demonstrate the power conversion efficiency (PCE) of 3.55% (open circuit voltage (Voc) = 0.62 V, short circuit current (Jsc) = 9.49 mA/cm2, fill factor (FF) = 60.4%), which is better than the device without interlayer (PCE = 2.95%, Voc = 0.60 V, Jsc = 8.11 mA/cm2, FF = 60.6%). This is due to that the reduction of a Schottky barrier at the cathode interface. Conventional type PSC with PVPy-ZW (3.45%) at the cathode interface also exhibit better the PCE compared to that of the device without interlayer (2.88%). Most increase in the PCE of the devices with interlayer is resulted from enhancement of the Jsc.

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