Efficient $p-i-n$ type organic solar cells incorporating 1,4,5,8-naphthalenetetracarboxylic dianhydride as transparent electron transport material

The implementation of proper charge carrier transport materials in $p-i-n$ type organic solar cells strongly influences the device performance. Our investigation focuses on the substitution of the standard layer sequence used at the side of electron transport, usually consisting of either $C60$/exciton blocking layer/metal or $n-C60$/metal by a layer sequence including a window layer. Here, we evaluate the transparent electron transport material 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), which guarantees a loss free charge extraction from the active materials due to a good energy level alignment as well as exciton blocking due to its wide bandgap. It is demonstrated that upon the exchange of the electron transport layer $n-C60$ for $n$-NTCDA, the solar power conversion efficiency of a $p-i-n$ device can be increased by 10%.