Nanocrystalline Ga-doped ZnO thin films for inverted polymer solar cells

• Ga-doped ZnO nanocrystalline thin films have been synthesized by sol–gel method.
• The grain size of Ga-doped ZnO is smaller than that of ZnO.
• We fabricated solar cells with Ga-doped ZnO as an electron transport layer.
• The best device configuration exhibits a power conversion efficiency of 3.25%.

Nanocrystalline ZnO and Ga-doped ZnO thin films have been prepared by sol–gel spin coating technique. X-ray diffraction results indicated that the grain size of Ga-doped ZnO is smaller than that of ZnO. The EDAX analysis confirmed that Zn, O and Ga elements are present in the samples. HRTEM image shows the formation of ZnO and Ga-doped ZnO nanocrystalline thin films with an average grain size of 22.5 and 12.5 nm. Inverted polymer solar cell containing Ga-doped ZnO as an electron transport layer with device structure ITO/Ga-doped ZnO/poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM)/MoO3/Al has been fabricated. The power conversion efficiency of inverted polymer solar cell with Ga-doped ZnO is 3.25%, which is higher than that of ZnO (1.96%).

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