Toward Faster Organic Photodiodes: Tuning of Blend Composition Ratio

The ability of a light-sensor to detect fast variation in incident light intensity is a vital feature required in imaging and data transmission applications. Solution-processed bulk heterojunction (BHJ) type organic photodiodes (OPDs) have gone through key developments, including dark current mitigation and longer linear dynamic range. In contrast, there has been less focus on increasing OPD response speed (f(-3dB)). Here, bulk heterojunction OPDs based on electron-donating polymer poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3 ',2 '-h][1,5]naphthyridine-2,7-diyl] (or PTNT) and electron-accepting phenyl-C-71-butyric acid methyl ester (or PC71BM) are reported. The intrinsic charge transport characteristics required for fast speed OPDs are discussed, and an analytical model for the same is developed. The OPDs present 0.8 MHz f(-3dB) under no applied voltage bias for a typical blend ratio of 1:1 by weight. It is shown that balanced electron and hole mobility is a critical criterion for faster speed OPDs, which can be realized by tuning the composition ratio of the bulk heterojunction. By tuning PTNT and PC71BM blend ratio, the f(-3dB) was successfully raised by more than quadruple to 4.5 MHz. The findings provide a tool to set device architecture for faster next-generation light sensors.

Automated summary

A study on bulk heterojunction OPDs based on PTNT and PC71BM is presented, with a f(-3dB) response speed of 0.8 MHz and the ability to increase it to 4.5 MHz by tuning the blend ratio, offering a new approach for faster next-generation light sensors.