Abstract
Indoor photovoltaics (IPV) using dye-sensitized solar cells (DSCs) is one among the most promising ambient energy harvesting technologies used to realize self-powered Internet of Things (IoT), consumer electronics and portable devices. The emergence of new generation Cu(ii/i) redox electrolytes used with co-sensitized organic dyes enables DSCs to realize higher open circuit photovoltages (V-oc) and power conversion efficiencies (PCE) under indoor/ambient illumination. Even though Cu(ii/i) electrolytes are promising candidates, the recombination of electrons from the conduction band and sub-bandgap states to the oxidized Cu(ii) species and slower regeneration of Cu(ii) at the counter electrode limit their performance. Taking inspiration from the asymmetric redox behaviour exhibited by the conventional iodide/triiodide electrolyte, which is efficient in inhibiting the undesirable recombination process, we introduced an alternative strategy of modifying the coordination environment of Cu(ii) metal center using the 2,9-dimethyl-1,10-phenanthroline (dmp) ligand. The resulting dual species [Cu(ii)(dmp)(2)Cl](+)/[Cu(i)(dmp)(2)](+) electrolyte exhibited an improved lifetime both under full sun and indoor illumination and better regeneration at the counter electrode. Employing this asymmetric dual species Cu(ii)/Cu(i) electrolyte with the co-sensitized D35:XY1 dyes, we realized a record PCE of 35.6% under 1000 lux warm white CFL illumination.