Enhanced the cell performance with morphology of ZnO nanoparticles and surface treatment for organic photovoltaic cells

Abstract

Spherical and rod-shaped zinc oxide (ZnO) nanoparticles were synthesized through modified sol-gel method to investigate the morphological effect in the buffer layer of inverted organic photovoltaic cells (OPVs). And we survey the influence of surface state on buffer layer by using zinc acetate dehydrate in methanol (zinc acetate post-treatment). The best power conversion efficiency (PCE) was exhibited in the device fabricated by using rod-shaped ZnO nanoparticles with zinc acetate post-treatment. Because of the 1-dimensional rod particles were acted as an appropriate bridge to promote the electron mobility and the zinc acetate post-treatment affected to the resistance in the device. By improving the resistance, the device of current density (Jsc) and fill factor (FF) were increased. Thus, the PCE of device were best result. Also, we studied the specific surface area with four-type ZnO buffer layer. Among them, the sample NM, which was made up of a 50/50 wt. % mixture of spherical ZnO and rod-shaped ZnO nanoparticles, has the high specific surface area and rough structure. The high surface area in buffer layer induced the fast electron transfer in OPVs. Also, the rough structure increased the contact area at the interface. So, it is occurs that the series resistance (Rs) of the device was decreased. By decreasing of the Rs, the Jsc and FF wer improved and the highest PCE is achieved for 2.75 % under 100mW/cm2 at AM 1.5 G simulated solar emission. The analyses were carried out by using TEM, FE-SEM, AFM, BET, XRD, current density-voltage characteristics and IPCE.