Tuning of Molecular Aggregation and Photoresponse of Narrow- band Organic Photodetectors

It is a great challenge to find suitable organic materials for developing narrow-band absorption organic photodetectors (NBA-OPDs) working in the deep-red and near-infrared spectral regions. In general, if dye molecules can form J-aggregates, their maximal absorption peak will red-shift and become narrower. In this work, a suitably structured pyrrolopyrrole cyanine (PPCy) with this unique property is realized for use in narrow-band photodetectors. It was found that the Coulomb and charge-transfer (CT) couplings of J-aggregates of PPCy can be tuned by the complexing boron group. Using poly[N,N '-bis(4-butylphenyl)-N,N '-diphenylbenzidine] (poly-TPD) as the donor and PPCy as the acceptor, the bulk heterojunction blends were prepared. The crystallinity and the crystal size of PPCy in the active layer can be changed by adjusting the weight ratio of the donor and the acceptor. Thus, the charge carriers' transportation in the device can be regulated. Furthermore, organic photodetectors with an adjustable narrow spectral response (full width at half-maximum, FWHM, 55-148 nm) in the 600-800 nm range have been prepared. In self-powered mode, the device's maximum specific detectivity (D*) is 2.1 x 1013 jones, which is the largest value among the reported NBA-OPDs in this spectral range. Moreover, when the mass ratio of poly-TPD and PPCy-1 is 2:1, the device exhibits the narrowest FWHM of 55 nm, an ultrafast response speed with a rise time of 0.4 mu s and a decay time of 0.8 mu s, and the maximum linear dynamic range of 168 dB. This work paves the way to construct a high-performance NBA-OPD by tuning the molecular aggregation of PPCy.