Thicker vs Thinner: Impact of Photoanode Thickness on Recombination Dynamics and Indoor Photovoltaic Performance in Dye-Sensitized Solar Cells

Abstract

The unique observation of enhanced photovoltaic performance in dye-sensitized solar cells (DSCs) under indoor/ambient illuminations using thinner electrodes devoid of scattering layers led us to undertake a comprehensive optimization of the thickness of the photoanode (TiO2 active layer) for high-performing DSCs employing the recently introduced hole-free spacer-free (HF-SF) device architecture. Devices with an average active layer thickness of 1, 2, 4, 6, and 8 μm were fabricated, and we observed dramatic variation in photovoltaic performance under one sun (100 mW/cm2) and indoor illumination (compact fluorescent lamp, CFL). While the 6 μm device outperformed others with a power conversion efficiency (PCE) of 9.56% under standard AM 1.5G one sun, surprisingly, the 2 μm device delivered a PCE of 34.65% under standard 1000 lux CFL illumination and a PCE of 35.02% under a much lower realistic intensity of 100 lux. With improvement in open-circuit voltage (Voc) being the primary factor for the elevated PCE exhibited by the 2 μm device, an in-depth analysis of the interfacial charge transfer dynamics is carried out to explain the obtained results. Further, benefiting from the enhanced transparency of the thinner (2 μm) device, it unveils innovative possibilities for applications in building-integrated photovoltaics (BIPV), as well as bifacial and multijunction devices.