UV-Ozone Treatment on Cs₂CO₃ Interfacial Layer for the Improvement of Inverted Polymer Solar Cells

Inverted configuration polymer solar cells (IPSCs) were prepared by using Cs₂CO₃ modified indium tin oxide (ITO) substrates as cathode and MoO3/Al as anode, ITO/Cs₂CO₃/P3HT:PCBM/MoO₃/Al. The interfacial Cs₂CO₃ layers were conducted with annealing treatment and different time UV-Ozone treatment. The power conversion efficiency (PCE) of IPSCs was improved to 1% when the UV-Ozone treatment time is 15 minutes, with the open-circuit voltage of 0.48 V, short-circuit current density of 5.4 mA/cm², and fill factor of 39%. The improvement of IPSCs should be attributed to the increased electron transporting and collection ability of Cs₂CO₃ layer induced by UV-Ozone treatment. The underlying mechanism of PCE improvement was discussed in terms of series and shunt resistance of cells induced by UV-Ozone treatment on Cs₂CO₃ layer, and the mole ratio of Cs to O of Cs₂CO₃ layer with different UV-Ozone treatment was investigated by scanning electron microscopy operating in the mode for in situ energy dispersive X-ray (EDX) spectra.