Achieving efficient and stable organic solar cells by using polyethylene glycol to modulate the crystallization and distribution of the active layer

Abstract

The crystallization and distribution of the materials in the active layer has a large effect on performance of solution-processed bulk heterojunction organic solar cells (OSCs). In this work, polyethylene glycol (PEG) is doped to the active layer as a common and inexpensive additive to modulate the crystallization and distribution of the material in the vertical direction. The effect of the addition of PEG on the active layer is confirmed by measuring the contact angle, grazing-incidence wide-angle x-ray scattering, and surface morphology. A performance improved device with power conversion efficiency (PCE) of 11.30% was achieved by doping 4 wt% PEG, which has 20% improvement over control devices (9.44%). It is important to note that the devices show strong tolerance to film thickness, the unpackaged devices with 300 nm thick active layer exhibit PCE of 8.58% (with PCE of ~80% compared with control devices). Also, devices show strong tolerance to high humidity environment, devices placed in 60% RH for 10 d still has 80% PCE. Moreover, green solvent was used to investigate the effect of PEG on the preparation of the device in the atmosphere, devices doped with PEG exhibit greater tolerance to the environment in preparation. This work provides a convenient way to improve device performance, tolerance to thickness, and stability at high humidity.