Synergetic effect of TiO2/ZnO bilayer photoanodes realizing exceptionally high VOC for dye-sensitized solar cells under outdoor and indoor illumination

Abstract

Harnessing energy from the surrounding light using indoor photovoltaics has gained momentum to address the carbon footprint resulting from used and dead batteries. Dye-sensitized solar cells (DSCs) have emerged as one of the most efficient and sustainable indoor light harvesting alternatives which can significantly reduce the environmental impact of batteries. Energy harvesting and managing circuits in these devices demand higher open circuit potentials (V_OC). Nevertheless, recombination losses frequently lower the open-circuit potential in DSCs, especially when illuminated indoors. We present an innovative TiO₂/ZnO bilayer architecture capable of delivering higher V_OC by carefully controlling the conduction band (CB) position and recombination losses. By sensitizing this innovative bilayer electrode with MS5 dye and a [Cu(dmp)₂]^1+/2+ redox mediator, we achieved a record V_OC of 1.27 V from a single junction device under Air Mass 1.5 Global (AM 1.5G), 100 mW cm⁻² solar irradiation and 1.295 V under higher intensity LED light (200 mW cm⁻²). These bilayer devices also demonstrated impressive V_OC of 1.025 V under 1000 lux compact fluorescent light (CFL) and light emitting diode (LED) illumination and could autonomously power a temperature sensor using a single device of 0.24 cm² active area. This work highlights the potential of modifying the semiconductor and device architecture to achieve higher V_OC in DSCs, which is essential for integrating these photovoltaic devices with smart IoT devices making them autonomous and sustainable.