Photocapacitive Electrostimulation with Hybrid Silicon/Organic Heterojunction Devices

Wireless electrostimulation by silicon photodiodes[1], as well as with organic photocapacitive devices[2,3] has been reported earlier, by <i>in-vitro</i> and <i>in-vivo</i> measurements on single cells and tissues. Organic electrolytic photocapacitor (OEPC) devices can be fabricated on micrometre-thin flexible substrates, with the entire active device stack thinner than 100 nm. Even though large optical absorption coefficients of organic materials allow for very thin and conformable devices, their inherently lower photo-conversion efficiencies require relatively large, millimetre-scale devices for effective stimulation. Silicon photodiodes, due to order of magnitude higher photo-conversion efficiencies, can be scaled down to a size of tens of micrometres while still being able to effectively stimulate. However, silicon photodiodes are based on high thermal budget dopant-diffusion and annealing processes, time-consuming and complex steps which in turn increase per unit cost of the devices[4]. We will present novel hybrid inorganic/organic photovoltaic-like devices based on <i>n</i>-type silicon as a substrate and a photo-active material and spin-coated and crosslinked PEDOT:PSS as a hole-collecting contact, with the heterojunction region being responsible for the charge separation and PEDOT:PSS additionally enhancing the capacitive properties of the device. Such solution-processed hybrid devices retain high photo-conversion efficiencies of traditional silicon <i>pn</i> homojunction photodiodes, yet can be fabricated cheaply and rapidly, enabling quick turnover times for device customization when being used as test beds for in-vitro experiments. We will demonstrate enhanced efficiency, spatial resolution and stability in aqueous environments of hybrid devices in comparison to purely organic OEPCs by measurements of the 3D transductive extracellular potential and corresponding E-fields. In addition, we will show in-vitro photo-induced modulation of the cell membrane potential of the human embryonic kidney (HEK) cells with heterologously expressed voltage-gated K+ channels, in comparison with OEPC devices.<br/><br/><b>References:</b><br/>[1] Mathieson, K., Loudin, J., Goetz, G. <i>et al.</i> Photovoltaic retinal prosthesis with high pixel density. <i>Nature Photon</i> <b>6</b>, 391–397 (2012). https://doi.org/10.1038/nphoton.2012.104<br/>[2] Rand, D., Jakesova, M., Lubin, G., Vebraite, I., David-Pur, M., Derek, V., Cramer, T., Sariciftci, N.S., Hanein, Y., Glowacki, E.D., Direct Electrical Neurostimulation with Organic Pigment Photocapacitors, <i>Adv Mat </i>vol.<i> </i>30, <b>25, </b>1707292 (2018). https://doi.org/10.1002/adma.201707292<br/>[3] Silvera Ejneby, M., Jakesova, M., Ferrero, J.J. <i>et al.</i> Chronic electrical stimulation of peripheral nerves via deep-red light transduced by an implanted organic photocapacitor. <i>Nat. Biomed. Eng</i> <b>6</b>, 741–753 (2022). https://doi.org/10.1038/s41551-021-00817-7<br/>[4] K. A. Nagamatsu, S. Avasthi, J. Jhaveri and J. C. Sturm, "A 12% Efficient Silicon/PEDOT:PSS Heterojunction Solar Cell Fabricated at &lt;100 °C," in <i>IEEE Journal of Photovoltaics</i>, vol. 4, no. 1, pp. 260-264, Jan. 2014, doi: 10.1109/JPHOTOV.2013.2287758.