Unraveling Energetic Disorder in Organic Bulk Heterojunction Photovoltaics by Capacitance-Voltage Spectroscopy

Organic semiconductors possess an intrinsic energetic disorder characteristic, which holds an exceptionally important role for understanding organic photovoltaic (OPV) operation and future optimization. We performed illumination intensity dependence of capacitance-voltage (C-V) measurements in PIDTDTQx:PC70BM based organic bulk heterojunction (BHJ) photovoltaics in working conditions. Energetic disorder profiles for the photo-active layer, PIDTDTQx:PC70BM, changed significantly when different interfaces were involved. The effects of energetic disorder that could be reflected from C-V profiles are incorporated through an exponential or Gaussian model of density of states (DOS), or a combination of these two. Results underlie that an identical organic blend in BHJ solar cells exhibits different energetic disorder when it interacts with various interfaces. It may, thus, has a certain impact on OPV performances, such as open-circuit voltage (V_oc ). Our study provides device physicists a different perspective view for tailoring the organic energetic disorder parameter via interfaces in order to enhance photo-electron conversion efficiencies (PCE).