Naturally-Sensitized Photoanodes for Molecular Photovoltaics
thesisposted on 2020-08-01, 00:00 authored by Hisham Ageel Maddah
Naturally-sensitized photoanodes in dye-sensitized solar cells (DSSCs) are promising alternatives to enhance photoabsorption, electron excitation/injection, but voltage loss remains a challenge. In this work, we focus on understanding perovskite cosensitization leveraging forward charge transport to address the voltage loss arising from ITO/TiO2 junction’s built-in potential in bio-sensitized DSSCs. The 𝛽-carotene-sensitized TiO2 photoanode modified with added MAPbI3 co-sensitizer cause an upward shifting in TiO2 Fermi level (EF). This phenomenon is predominantly attributed to increased initially injected electrons due to low MAPbI3 bandgap (~1.87 eV) and high visible-light absorption. Thermal annealing of TiO2/MAPbI3 heterostructure ensures existing of both: (i) covalent bonding contributing to ultrafast interfacial charge separation, and (ii) strong van der Waals interactions between donor/acceptor species at TiO2/MAPbI3 interface facilitating electron injection. Enhanced charge separation and injection mechanisms at the TiO2/MAPbI3 interface increase the effective density of states (>2.46x1021 cm-3) in TiO2 conduction band (CB) and hence decrease its work function to 4.82 eV. The decrease in TiO2 work function suppressed CB bending at the ITO/TiO2 junction, which minimized the photoinduced electrostatic potential barrier up to 13.1%. This lessened Schottky barrier (𝜙𝑆𝐵𝐻<0.52 eV) only allow electrons tunneling, while inhibited back-electron transport reduced both current leakage and voltage loss yielding in high Voc increased by 120% and PCE (>240%). MAPbI3 incorporation also broadened photoanode absorbance by 2-fold, paving the way towards perovskite cosensitization to avoid voltage loss from bio-integrated photoanodes for photovoltaic and optoelectronic applications.