**Acknowledgements**

This work is supported by the by the Ministry of Science & Technology, Government of the People's Republic of Bangladesh under the Special Allocation Research project for Science & Technology, FY 2019-2020, entitled, "Development of nanotechnology based solar cells using low cost natural dyes extracted from vegetables and the effect of gamma radiation on its performance", (Ref. No.: 39.00.0000.009.06.024.19/ID-478-494).
