Excess current/capacitance observation on polymer–fullerene bulk heterojunction, studied through I–V and C/G–V measurements

Excess current/capacitance behavior was observed on the Ag:Ca/P3HT:PCBM/PEDOT:PSS/ITO structure and the associated mechanism(s) were identified by performing both dc current–voltage (I–V) and ac capacitance–conductance–voltage (C/G–V) measurements in dark and light exposure, respectively. The excess current/capacitance issue, originated owing to a minority carrier injection, has manifested itself as conductivity modulation in I–V and decrease in capacitance in C–V at a sufficiently large forward bias. Satisfactory analysis in I–V as transport property and C(G)–V as storage feature were carried out on Ag:Ca/P3HT:PCBM/PEDOT:PSS/ITO structure.

► The work discusses conductivity modulation on polymer–fullerene bulk heterojunction.
► Energy band diagram and its equivalent circuit are proposed.
► Carrier conduction paths are identified.
► Equivalent capacitance and conductance terms for the proposed circuit are derived.