Improvement in power conversion efficiency and long-term lifetime of organic photovoltaic cells by using bathophenanthroline/molybdenum oxide as compound cathode buffer layer

We demonstrate response and lifetime improvements for organic photovoltaic (OPV) by using organic bathophenanthroline (Bphen) and inorganic molybdenum oxide (MoO3) as a compound cathode buffer layer (CBL). Not only power conversion efficiency (PCE) increases by 27% but also working and storage lifetimes extend at least 10 and 60 times respectively comparing with PV cell with 5 nm thick Bphen as CBL. The optimized PV structure is ITO/CuPc (20 nm)/C60 (40 nm)/Bphen (2 nm)/MoO3 (5 nm)/Al and the CBL of the reference device is 5 nm Bphen without MoO3 layer. The achievement of PV performance and lifetime improvement by introducing such a compound CBL is attributed to appropriate level alignment between C60, Bphen and MoO3, and stable inorganic MoO3 can prevent from superior oxygen and moisture diffusion into the C60 acceptor layer. The detailed working mechanism of the compound Bphen/MoO3 CBL in the OPV cells is also argued.