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Abstract
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The principal aim behind doping of cadmium sulfide (CdS) quantum dots (QDs) by gadolinium (Gd) cations and
fabrication of core (CdS)-shell (cadmium selenide (CdSe)) nanostructures was to increase the performance in the
QD-sensitized solar cells (QDSSCs). By simultaneously doping with Gd and designing the core–shell nanostructures,
the well-acted photovoltaic cells were fabricated where short current density (Jsc) = 14.91 mA/cm2,
fill factor (FF) = 64.9%, open-circuit voltage (Voc) = 707 mV, and power conversion efficiency (η) = 6.84%. The
addition of zinc sulfide (ZnS) layer onto TiO2/Gd-doped CdS@CdSe photoanodes improved the cell parameters
including Jsc, FF, Voc, and η up to 16.34 mA/cm2, 65.24%, 710 mV, and 7.57%, respectively. The presence of
Gd3+ in the the CdS crystal lattice promotes the charge injection rate from the conduction band (CB) of CdS to CB
of TiO2 by successive trapping and losing the photoinduced electrons due to its unique half-filled electron
configuration in valance f orbitals. Upon creating the Gd3+ doped-CdS@CdSe structures, the exciplex states were
formed to reduce the effective bandgap of QDs and expand the light-harvesting range in visible wavelengths. The
comparison of relative chemical capacitance (Cμ) under both dark and illumination conditions, obtained from
electrochemical impedance spectroscopy (EIS) measurements, revealed that the Gd3+ doping of QDs can shift the
CB level of TiO2 and, thereby, elevate the Voc. Moreover, the EIS and photoluminescence (PL) spectroscopy
showed that doping suppresses the charge recombination at the photoanode/electrolyte interfaces and also
improves Jsc and η in the fabricated cells
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