High performance Organic Photodiode with Wide Linear Dynamic Range: The Role of Crystalline Orientation

Abstract

A new polymeric semiconductor, which can effectively extend linear dynamic ranges (LDRs) of organ-ic photodiodes (OPDs), was developed. Copolymers based on alkylthio-substituted benzo[1,2-b:4,5-b’]dithiophene (BDT) are synthesized in conjunction with fluorinated terthiophene (BDT-Th-3T) or alkylter-thiophene (BDT-Th-3AT). When deposited onto an ITO/polyethylenimine ethoxylated (PEIE) substrate, both copolymer thin films render apparent face-on orientations as indicated in two-dimensional grazing incidence X-ray diffraction (2D-GIXD) results, and especially among them, BDT-Th-3T thin films show much im-proved crystalline properties. This is because the molecular structure of BDT-Th-3T shows a higher molecular planarity induced by non-covalent intramolecular interaction and small steric hindrance, which are proved from UV-Vis-NIR absorption and Raman spectroscopy studies, respectively. BDT-Th-3T polymers effective-ly maintain their crystalline properties when are blended with non-fullerene acceptors and form a bulk hetero-junction (BHJ) of a percolating network composed of face-on-oriented donors and acceptors, which is favor-able for charge carrier transports in a vertical direction of the device. As a result, the optimized OPD shows a high specific detectivity over 10^13 jones and an unprecedentedly wide LDR of 232 dB. It is demonstrated that the wide LDR is originated from high charge transporting property of the polymer, which induces a high saturation photocurrent of BHJ