Fabrication of inverted bulk heterojunction organic solar cells based on conjugated P3HT:PCBM using various thicknesses of ZnO buffer layer

Recently, there has been tremendous progress among the researchers all over the world in the development of polymer-based organic solar cells as a clean and safe energy source. Besides, it has also attracted a great attention due to its inexpensive manufacturing cost and environment-friendly energy conversion capability. However, they still have low efficiency and the unstable because organic materials are easily oxidized by humidity and UV light under the atmosphere environment. The objective of this study was to investigate the effects of different thickness of the ZnO buffer layer on the general performance of the bulk heterojunction organic solar cell devices with configuration indium tin oxide/zinc oxide buffer layer/poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester/gold (ITO/ZnO/P3HT:PCBM/Au). ZnO film acts as a protection layer to prevent the interface of photoactive layer by UV light from the oxidation and to reduce the energy barrier for easily transferring electron between collecting electrode and the LUMO level of the organic acceptor. Also, ZnO film block holes in P3HT from being recombined with electrons in collecting electrode. It is observed that the power conversion efficiency is significantly dependent on the thickness of the buffer layer. The solar cell performance of a short-circuit current density of 1.599 mA/cm2, an open-circuit voltage of 119 mV and a fill factor of 20.85%, with a power conversion efficiency of about 0.0432% under AM 1.5 illumination (100 mW/cm2) is obtained when the thickness of the buffer layer is optimized.