Electric field assisted spray deposited MoO3 thin films as a hole transport layer for organic solar cells

• Spray deposition of MoO3 in the presence of electric field was done.
• Formation of different nanostructures in the presence of electric field.
• Crystallinity of MoO3 layer get enhanced in the presence of electric field.
• Reduced defects after applying DC voltage.
• Improved efficiency of organic solar cell by applying DC voltage.

Spray deposition of molybdenum trioxide (MoO3) hole transport layer under a DC voltage (500 V and 1000 V) applied to the nozzle yielded orthorhombic phase of MoO3 (α-MoO3) with no other phases present. The films had uniform, compact surface morphology with reduced roughness, increased transmittance and band gap as compared to those for spray deposited MoO3 layer deposited without applying the DC voltage. In addition an increase in the work function was also observed possibly due to the change in the nanostructures formed on the surface. XPS result showed that the application of DC voltage during spray deposition reduced the oxygen vacancies. The reduced potential barrier height between MoO3 and P3HT layer can be useful in organic bulk-heterojunction solar cell (ITO/MoO3/P3HT:PCBM/Al). This was indeed proven by organic bulk-heterojunction solar cell fabricated using the electric field assisted spray deposited MoO3 layer yielding 2.71% power conversion efficiency with short circuit current density (JSC) of 10.0 mA cm−2, open circuit voltage (VOC) of 0.57 V and fill factor (FF) of 47.4%. The organic solar cell fabricated using electric field assisted spray deposited MoO3 layer showed an improved performance as compared to the standard spin coated solar cell.

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