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.
AdvisorBehura, SanjayBerry, Vikas
Degree GrantorUniversity of Illinois at Chicago
Degree namePhD, Doctor of Philosophy
Committee MemberCheng, Gang Liu, Ying Daly, Matthew
Submitted dateAugust 2020