Enhancement of organic solar cell efficiency by altering the zinc oxide photoanode nanostructure morphology

Abstract

The current paper examines the effects of zinc oxide nanostructure configurations, as photo-anode formations of organic solar cells, on the performance of power conversion. To this end, some experiments were conducted during which a near band edge emission red shift of ~ 0.11 eV from nanoparticles to vertically oriented nano-rods was observed. This bandgap narrowing promotes transferring of photo-excited electrons towards the conduction band of photo-anode. A ~ 48% decrease in the deep level emission intensity revealed a smaller non-radiative waves emission due to lower level of crystal disorder. Using vertically oriented zinc oxide nanorods as photo-anodes, the photovoltaic efficiency of the organic solar cell improved considerably. The nano-rod-structured photo-anodes showed a 0.22 V rise in the open-circuit voltage, from 0.76 to 0.98 V, and a 2.08 times increment in the overall conversion performance, compared to the zinc oxide nanoparticle-structured photo-anodes. This superior performance is attributed to a greater chance of charge recombination and light-trapping in the cells, more efficient light absorption, and high level of crystallinity that grants easier electron mobility for vertically oriented zinc oxide nanorods. Moreover, a lower charge-transfer resistance (0.85 Ω) was achieved due to better electro-catalytic action for oxygen reduction for vertical nanorods compared to the other two zinc oxide configurations (1.62 Ω and 4.06 Ω). This boosted the cell performance by increasing the short-circuit current density (JSC). The fabricated solar cell may contribute to sustainable and environmentally friendly electricity generation process through reducing the consumption of non-renewable energy sources.