Improving Interfacial Charge-Transfer Properties of Quantum Dot-Sensitized Solar Cells via a Ce-TiO2 Interlayer

Abstract

Quantum dot-sensitized solar cells (QDSSCs) have attracted considerable attention due to their low fabrication cost, tunable band gap, and high light harvesting capability. However, strong charge recombination at the FTO/TiO2 interface and inefficient electron transport remain the main obstacles limiting their photovoltaic performance [1–4]. In this study, an x% Ce-TiO2 interlayer (x = 1.5, 2.5, 5, 7.5, and 10%) was inserted between the FTO substrate and the mesoporous TiO2 layer to overcome this problem. The FTO substrates were immersed in a dilute TiCl4 solution containing different concentrations of cerium cations and heat-treated at 70 °C for 1 h. Subsequently, a mesoporous TiO2 layer was deposited on the annealed substrates, followed by sequential sensitization with CdS/CdSe/ZnS quantum dots (QDs) using the sequential ionic layer adsorption and reaction (SILAR) method (x% Ce-TiO2/TiO2/CdS/CdSe/ZnS). FE-SEM and EDX analyses confirmed the homogeneous porous morphology after QDs sensitization. Photocurrent density-voltage (J-V) measurements under AM 1.5G irradiation showed that the photovoltaic performance gradually improved with increasing Ce content. The modified device with 10% Ce-TiO2 showed the best performance, achieving a Voc of 0.54 V, Jsc of 17.16 mA/cm2, FF of 0.481, and a power conversion efficiency (PCE) of 4.46%, compared to 3.15% for the reference cell without coating. These improvements are attributed to the improved electron transport and suppression of interfacial charge recombination caused by the Ce-TiO2 interlayer.