The effects of annealing rate and morphology of sol-gel derived zinc oxide (ZnO) thin films on the performance of inverted polymer solar cells (IPSCs) are investigated. ZnO films with different morphologies are prepared at different annealing rates and used as the electron transport layers in IPSCs. The undulating morphologies of ZnO films fabricated at annealing rates of 10 • C/min and 3 • C/min each possess a rougher surface than that of the ZnO film fabricated at a fast annealing rate of 50

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... C/min. The ZnO films are characterized by atomic force microscopy (AFM), optical transmittance measurements, and simulation. The results indicate that the ZnO film formed at 3 • C /min possesses a good-quality contact area with the active layer. Combined with a moderate light-scattering, the resulting device shows a 16% improvement in power conversion efficiency compared with that of the rapidly annealed ZnO film device.