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 C ₆₀, 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/MoO ₃ CBL in the OPV cells is also argued. © 2013 Elsevier B.V.