Photomultiplication Behavior of Chlorophyll-Based Photodetector under Biased Voltage.

ABSTRACT

In this study, we fabricated a photodetector (PD) with two types of chlorophyll derivatives, namely, zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (ZnChl) and methyl 131-deoxo-131-dicyanomethylene-pyropheophorbide-a (H2Chl'), via a two-step drop-coating process. In the absorption range of ZnChl/H2Chl' films, the maximum external quantum efficiency of ZnChl/H2Chl'-based devices reached 1363% at -8 V and 1345% at 2.5 V, exhibiting the photomultiplication (PM) phenomenon. The PM phenomenon of ZnChl/H2Chl'-based devices is attributed to hole tunneling injection from the external circuit assisted by electron accumulation in the ZnChl and H2Chl' under light illumination. Through the investigation of the responsivity (R) of ZnChl/H2Chl'-based devices, it has been found that achieving a high R is easier under forward bias compared with reverse bias (7706 mA/W at -8 V and 7629 mA/W at 2.5 V). The organic PDs based on ZnChl/H2Chl' exhibit PM behavior, offering a promising approach to improve the device's responsivity.