The role of etching current density and porous structure on enhanced photovoltaic performance of ZnO/PS heterojunction solar cells

Abstract

The paper reports the fabrication of zinc oxide/porous silicon (ZnO/PS) heterojunction solar cells based on porous material and the effects of etching current density and porous structure on the performance of these solar cells. PS samples were produced by electrochemical etching on a p-type crystalline-silicon (c-Si) wafer with boron (B) doped and (111) orientation. The etching process was carried out in a HF:C2H5OH (1:3) electrolyte solution at different etching current densities of 5, 10, 15, and 25mA/cm(2) for 15min at room temperature (RT). ZnO nanoparticles synthesized by sol-gel method were coated on PS layers by the sol-gel spin coating technique at a speed of 300rpm for 20s at RT for fabrication of ZnO/PS heterojunction solar cells. The structural analyses were performed using a field emission scanning electron microscope. Depending on the increase of etching current density, the pore diameter and porosity in the etched structures increased approximately from 200 to 920nm and from 19 to 62%, respectively. Reflection characteristics of ZnO/PS heterojunction solar cells were determined using reflection measurements. The lowest optical reflection was obtained in ZnO/PS heterojunction solar cell with PS layer formed at high etching current density. The dark I-V measurements indicated that all the solar cells exhibited a typical rectifying behavior, and the ideality factor increased with the increase of etching current density. Light I-V measurements were performed under AM1.5G conditions. The short circuit current, open circuit voltage, and energy conversion efficiency (eta) increased with the increase of etching current density. The best photovoltaic performance was obtained in ZnO/PS heterojunction solar cell having the PS layer produced at high etching current density of 25mA/cm(2). The highest energy conversion efficiency of 6.05% was obtained in this solar cell. It was determined that the etching current density and porous structure are important parameters affecting the photovoltaic performance of ZnO/PS heterojunction solar cells.