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 C₆₀ 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.