Improving the performance of ITO/ZnO/P3HT:PCBM/Ag solar cells by tuning the surface roughness of sprayed ZnO

A simple hetero junction with configuration ITO/ZnO/P3HT:PCBM/Ag was fabricated by employing chemical spray pyrolysis technique for ZnO thin film and spin coating technique for polymer film deposition. Both ZnO and polymer deposition was conducted in ordinary atmospheric conditions. Roughness of ZnO layer was observed to be crucial parameter that determines overall performance of the device. Optimization of surface roughness of ZnO layer for better quality of the device was achieved through variation of spray parameters (viz., substrate temperature and spray rate). AFM analysis was effectively used to explore the surface roughness of ZnO layer. Structural, optical and electrical studies were also done for samples prepared at optimized condition. The best device under this study has open circuit voltage of 523 mV, short circuit current density of 8.32 mA/cm2, fill factor of 37% and efficiency of 1.62%. In order to demonstrate the potential of chemical spray pyrolysis technique for large area deposition, the optimized deposition conditions for small area (0.03 cm2) cell were extended for large area device (6.25 cm2). Indoor and outdoor measurements were also performed on large area device.