The researchers detailed their approach in a paper titled "Silicon Nanowire/Polymer Hybrid Solar Cell-Supercapacitor: A Self-Charging Power Unit with a Total Efficiency of 10.5%" published in Nano Letters.
First, they built a hybrid silicon nanowire/polymer heterojunction solar cell consisting of highly-ordered vertically aligned Si nanowires (about 250nm in diameter at an approximate pitch of 360nm in a hexagonal array) spin-coated with highly conductive PEDOT:PSS and later covered with a 200nm-thick silver finger grid as the front electrode while a 200nm-thick layer of aluminium served as a rear contact.
One thing the researchers documented was the use of a low temperature, chemical solution process to reduce the nanowire surface roughness, suppressing the charge recombination at the SiNW/polymer interface and enhancing the solar cell's power conversion efficiency to 13.39%.
They then built a polypyrrole-based supercapacitor affixed to the back of the solar cell. To do so, a titanium film was thermally deposited on the back side of the Si substrate, acting both as the rear electrode of the hybrid solar cell and one of the electrodes of the supercapacitor. Then polypyrrole films were electrochemically deposited on the titanium film to form a symmetric supercapacitor (using a porous polyethylene membrane as a separator and H3PO4/PVA (poly(vinyl alcohol)) gel as the electrolyte.