Our solid-state protein matrix is a resultant of an electrospinning process using only solvated BSA protein. The free-standing material has a fibrillar structure (Figure ) with a thickness of ~70 µm and it can contain a significant amount of water ~100-150 wt.%. The formed mat was then placed in an aqueous solution of Chl, resulting in spontaneous irreversible binding of the Chl molecules to the mat in a process we refer to as molecular doping (Figure ). As shown previously, this straightforward doping strategy results in highly doped protein mats with doping density in the order of 2-3×10 19 cm -3 . After the successful binding of the Chl molecules to the protein matrix, we investigated the mat's electrical properties. First, we measured the conductivity of the Chl-doped mat using electrochemical impedance spectroscopy (EIS) by laying the mat on gold finger electrodes with a separation distance of 1 mm (Figure ). By fitting the EIS measurement to an equivalent circuit (Figure , inset), we extracted a bulk conductivity value of 3.1 ± 0.6 mS•cm -1 for the Chldoped mat. For the light harvesting photocurrent generation type of measurements, we used current-time (I-T) measurements upon the application of a DC bias in the same experimental setup as for the EIS measurements, i.e., a terminal device with the mat bridging two gold electrodes. It is important to note that this configuration is symmetric, and it is not a solar cell configuration. During these measurements, we light-irradiated the mat using different wavelengths with the purpose of studying the photocurrent characteristic (Figure for a fixed bias of 1.5 V). As shown in the figure, we observed a drop in current under light irradiation. A decrease in conduction upon illumination, also known as negative photoconductivity, was previously observed in semiconductors, metal nanoparticles, carbon nanotubes, and even in protein-based materials (incorporated with metal nanoparticles). One main explanation for the negative photoconductivity phenomenon is based on a trapping effect, where impurities can trap the photo-induced carriers, resulting in a decrease in charge density. Such a trapping effect and other suggested mechanisms are expected to change the bulk conductivity across the material upon light irradiation. Importantly, our EIS measurements show identical bulk conductivity of the doped protein matrix under dark conditions and under light illumination (Figure ), and thus, the negative photoresponse in our material cannot be explained by the trapping phenomenon. Instead, as discussed below, all our solid-state measurements indicate the involvement of an anodic photocurrent process taking place next to the two electrodes in the solid state, with some similarities to common electrochemical photocurrent generation, whereas the protein matrix and its trapped water environment is fundamental in the electronic (hole) quenching process of the photocurrent (see discussion below).