High efficient inverted polymer solar cells with different annealing treatment

Inverted polymer solar cells (IPSCs) were fabricated with cesium carbonate (Cs2CO3) modified indium tin oxide (ITO) substrates as the electrode and molybdenum trioxide (MoO3) modified Al as the anode. The Cs2CO3 dissolved in 2-ethoxyethanol was spin-coated on ITO substrates, showing snowflake-like morphology characterized by the scanning electron microscope (SEM). The absorption, X-ray diffraction as well as the morphology of the active layer were measured before and after annealing treatment. The IPSCs with annealing treatments on the active layers and MoO3 layers exhibited the maximum power conversion efficiency (PCE) approaching to 2%, with open circuit voltage (Voc) of 0.57 V, short circuit current density (Jsc) of 8.8 mA/cm2 and fill factor (FF) of 38.7%. The performance of IPSCs was dramatically decreased by annealing treatment after the deposition of Al cathode, which may be due to the diffusion of Al atom crossing the MoO3 layer forming new channels for charge carrier collection. However, the new channels are not beneficial to the charge carrier collection, which is demonstrated from that the Jsc of IPSCs was evidently decreased from 8.8 to 4.6 mA/cm2 by annealing treatment after deposition Al layer. The annealing treatment after deposition of MoO3 could improve the interfacial contact to aid in electron extraction.

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► PCE of inverted polymer solar cells (IPSc) with Cs2Co3 modified ITO as cathode and MoO3/Al as anode is approaching to 2%.
► The snowflake-like morphology of Cs2CO3 was investigated by SEM.
► The annealing treatment before deposition Al layer has positive effect on improvement of IPSCs performance.
► EDX results directly demonstrate the vertical phase separation of P3HT:PCBM induced by annealing treatment.