Abstract
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•We study the structural of thin film of ZnO annealed at different temperatures.•The crystalline and structural quality of ZnO films increase at 150°C.•The active layer of inverted OPVs was deposited with two spin coating speeds.•Better performance of the devices was obtained with fast spin coating speed.•Performances of inverted type OPVs depend on the recombination process.
Structural of thin film of ZnO elaborated by sol–gel ZnO method, annealed at different temperatures were investigated by means of Photoluminescence and Raman spectroscopy analysis. The results show the formation of crystalline layer of ZnO after annealing at 150°C. This thin film provided an effective hole blocking layer and an increased interfacial area for electron collection. Inverted bulk heterojunction organic solar cells were fabricated using ZnO film as the electron collecting layer. The influence of spin coating speed of the active layer on the performance of inverted-type organic solar cells has been investigated. The organic photoactive layers consisted of Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-Phenyl-C71-butyric acid methyl ester (PC70BM) were spin coated onto ZnO thin film with two spin coating speeds at 600 and 2000rpm. Experimental results showed that the short-circuit current density (Jsc), the fill factor (FF) and power conversion efficiency (PCE) increase with increasing spin coating speed. This result may be attributed to reducing series resistance and recombination processes in thinner photoactive layer.
The impedance spectra of the devices were measured under illumination. A decrease in the charge recombination and the resistance of whole device were observed with the increase in the spin coating speed of the active layer.