Facilitating electron extraction of inverted polymer solar cells by using organic/inorganic/organic composite buffer layer

In this work, the performance of inverted polymer solar cells (PSCs) was enhanced by introducing an organic/inorganic/organic (OIO) composite electron-transporting layer (ETL) with the structure of poly ethylenemine (PEI)/SnO2/poly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9, 9-dioctylfluorene)] (PFN). The work function measurement and surface morphology indicate that OIO ETL modulates the energy level between active layer and cathode, and reduces the interfacial defects due to the poor contact between organic material and inorganic substance. Also, the OIO ETL could enhance the light absorption of active layer. Therefore, both a high short-circuit current density and fill factor are obtained in the devices owning an OIO ETL, which leads to a dramatic enhancement of device efficiency from 5.51% to 7.18%, accounting for a 30.30% increase. This novel concept of OIO ETL paves a new path for the future applications in the field of PSCs.