Multi-junction architecture is an attractive method to overcome the efficiency limit of single-junction photovoltaic solar cells. Series-connected multi-junction polymer solar cells (PSCs) have attracted much attention during the past decade. In this study, single and double layer polymer solar cells were fabricated incorporating copper oxide and zinc oxide nanoparticles (CuO and ZnO NPs) in the active layers. Thermal annealing treatment was
applied to the single and double junction devices at 200oC to optimize the nanoscale morphology. The single layer device produced 2.963% power conversion efficiency and it was reduced to 1.102% in the double junction solar cell. However, the enhanced morphological and optoelectronic properties attained by applying thermal annealing slightly increased the power conversion efficiency. Meanwhile, the external quantum efficiency
(EQE) increased from 32.4% to 37%, showing an enhancement of 12.4% with the thermal annealing treatment.
