Influence of Molybdenum Oxide Interface Solvent Sensitivity on Charge Trapping in Bilayer Cyanine Solar Cells

Bilayer organic solar cells based on trimethine cyanine donor and C-60 acceptor materials have been fabricated by coating the trimethine dye from solution on molybdenum oxide (MoO3) anode buffer layer. The choice of deposition solvent drastically influences device performance, with 2,2,3,3-tetrafluoro-1-propanol (TFP) reducing the fill factor and power conversion efficiency of the device by 36 and 21%, respectively, as compared to chlorobenzene. In the case of TFP, extraction of photogenerated charge carriers by linearly increasing voltage (photo-CELIV) and capacitance- voltage analysis revealed the formation of a hole trapping zone at the molybdenum oxide interface which is also responsible for the S-shape current-voltage curve under white light irradiation. The transient charge extraction signal originating from trapped holes at the MoO3 interface could be clearly distinguished from the one relating to hole mobility in cyanine films using photo-CELIV measurements with varying delay times.