Multiple electron transporting layers and their excellent properties based on organic solar cell

To improve the performance of inverted polymer solar cells based on a ternary blend of polymerthieno [3,4-b] thiophene/benzodithiophene (PTB7), [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) and indene-C60-bisadduct (ICBA), a two-layer structure of zinc oxide (ZnO) and Al-doped zinc oxide (AZO) nanoperticles is used to improve electron extraction. Comparing to ZnO, AZO has lower work function and thus provides larger built-in potential across the organic heterojunction, resulting in more efficient photo-current extraction and larger open circuit voltages. Optimum devices with ZnO/AZO nanoparticles show enhancement of both short circuit current and open circuit voltage, leading to a power conversion efficiency (PCE) of 8.85%. The argument of energy level buffering and surface morphology is discussed in the paper. Finally, using a trilayer electron transporting unit of ZnO/AZO/PFN, the interface dipole between the organic active layer and AZO is introduced. The PCE is further enhanced to 9.17%.