Determining the Role of the Molecular Weight of Poly(Ethylene Glycol) Additives in Perovskite Photodetectors

The performance of perovskite photodetectors was often tuned by changing the functional groups of polymeric additives, rather than their molecular weight to improve defect passivation. As a result of the steric effect of polymeric additives, we found that the molecular weight of poly(ethylene glycol) (PEG) additives played an important role in determining the perovskite crystal size, which increased from 470 to 550 nm with increasing molecular weight from 6k to 10k but declined back to 450 nm with further increasing molecular weight to 20k. The noise current, rather than the external quantum efficiency, was the dominant factor that can be tailored to improve the photodetection performance using PEG additives with different molecular weights. The photodetectors based on the 10k PEG additive exhibited a high specific detectivity of 1.9 x 1011 Jones, a linear dynamic range of 119 dB, and a frequency response -3 dB of 11.57 kHz. This work demonstrates an alternative approach by tailoring the molecular weight of polymeric additives to optimize the morphology of perovskite films for improved performance in perovskite photodetectors and other perovskite optoelectronic devices.