Transfer-Printed Nanoscale Poly(3-hexylthiophene-2,5-diyl) Layers for Organic Photodetectors

Solution-processed organic photodetectors (OPDs) with organic layers on the order of nanometers have received tremendous attention due to their advantages of low cost, light weight, flexibility, and simple fabrication. The relatively high dark current, which is ascribed to the inherent properties of the bulk heterojunction structure, limits further promotion of OPDs. In this work, we performed a systematic investigation on transfer printing technology (TPT) based on different electron blocking layers (EBLs) and active layers. We demonstrated that the surface morphology of transfer-printed layers determines the performance of OPDs. Compared with PBDB-T and MEH-PPV, a smooth and compact P3HT layer can be obtained by TPT. The results demonstrated that in addition to the energy level or absorption spectrum of the material, the mechanical property that the surface remains smooth after transfer printing needs to be added as a selection criterion for transfer-printed EBLs. The dark current was reduced by approximately 2 orders of magnitude compared with that of the OPD without an EBL based on three different active layers (including fullerene and nonfullerene systems), while comparable photocurrents were obtained. Consequently, a similar responsivity (R), an improved specific detectivity (D*), and an enlarged linear dynamic range for OPDs were observed with the insertion of transfer-printed P3HT. Finally, the effect of transfer printing on the photoresponse time was investigated, and the results demonstrated that transfer-printed EBLs slightly increased the photoresponse time of OPDs.