Study On The Flexible Solar Cell Based On The Small-bandgap Organic Material

Organic solar cells（OSCs）attract extensive attention in recent years owing to their light weight physical feature,easy preparation process and flexibility.Especially the flexiblity make OSCs promising in many fields.The limit of commercial use of OSCs is the lower PCE and stability.An inverted structure could effectively improve the stability of OSCs.But the preparation process of cathode buffer layer in OSCs is always undergo high annealling temperature condition.The high annealling temperature limits OSCs’application in the field of flexible electronics.In this work,we fabricate flexible OSCs devices based on small-bandgap semiconductor PTB-7 with high performance and stability.Firstly,cathode buffer layer（CBL）is very important for the performance of the inverted OSCs devices.TiO₂,Al₂O₃ and ZnO are frequently-used as CBL materials.Among them ZnO is an appealing CBL material due to its high charge mobility,low cost,environmentally friendly nature.But the most used method（sol-gel）always need a high annealing temperature（>300°C）to fabricate Zn O CBL.We fabricate high performance OSCs with ZnO film processed from the aqueous solution methode instead of sol-gel method based on PTB-7:PCBM.The result demonstrates that the PCE of OSCs with the configuration PET/ITO/ZnO/PTB7:PC₇₁BM/MoO₃/Ag based on 150°C processing temperature solution method could reach to 7.68%.On the other hand,our flexible OSCs device also exhibit desirable mechanical properties and reliability.The device could maintain 85%of it initial PCE after 240h under air ambient and keep 93%of it original PCE after 1000 bending cycles with a radius of 0.8cm.Secondly,we improved the performance of the flexible OSCs without raising the processing temperature by using PEIE to modify ZnO as CBL.The PCE of the OSCs device with the structure PET/ITO/ZnO/PEIE/PTB7:PC₇₁BM/MoO₃/Ag increased to8.12%,which is higher than PCE of the OSCs device with pure ZnO CBL.Studing the morphology,hydrophilia and transmittance of pure ZnO layer,pure PEIE layer,ZnO/PEIE bilayer and PEIE/ZnO bilayer,we found that modifying Zn O by PEIE could not only decrease the work function of ITO/ZnO but also smooth the ZnO films.The contact between CBL and actice layer is improved due to the smoother CBL and the performance is enhanced.