Abstract
Measuring the transient photoelectric signals (photovoltage or photocurrent) after optically perturbing dye-sensitized solar cells (DSSCs) can provide information about electron transport and recombination. Herein, the energetic distribution of trap states in different working areas of DSSCs (0.16 cm2vs. 1 cm2) and their impacts on charge transport and recombination were investigated by means of time-resolved charge extraction (TRCE), transient photovoltage (TPV) and transient photocurrent (TPC) measurements. The results indicated that increasing the working area deepened the energetic distribution of trap states (i.e., increased the mean characteristic energy kBT0), which hindered the electron transport within the photoanode, accelerated the electron recombination in high voltage regions, and reduced the charge collection efficiency. All abovementioned are the inherent reasons why the JSC in larger working area cells is significantly smaller than that in smaller area cells (11.58 mA cm−2vs. 17.17 mA cm−2). More importantly, as the investigation of high-efficiency large area solar cells is currently a promising research topic for new solar cells, we describe the importance of photoanode optimization to achieve high-efficiency DSSCs with large working area by improving charge collection efficiency.
Highlights
Electron transport dynamics and recombination kinetics are major determinants of the overall efficiency of dye-sensitized solar cells (DSSCs)
The overall efficiency of cells are largely determined by the electron transport and recombination kinetics, and the study of those kinetics in DSSCs is of great signi cance for improving the structure and materials of DSSC photoanodes, the short-circuit current density, and the power conversion efficiency (PCE) of cells
In addition to the increase in the RFTO, we demonstrate that the anode area strongly affects the density of trap states (DOS) distribution, electronic transport/recombination kinetics and charge collection efficiency
Summary
Electron transport dynamics and recombination kinetics are major determinants of the overall efficiency of dye-sensitized solar cells (DSSCs). Following electron injection of the photoexcited dye molecules (attached to the semiconductor nanoparticle surface) into the semiconductor conduction band (cb), the electrons travel through the TiO2 lm These electrons are collected at the back contact unless they recombine with the redox species in the electrolyte (eÀ + S+ / S) or recombine with the oxidised dye molecules bound to the semiconductor surface (eÀ + Ox / Red).[1,2,3] Because of the rapid regeneration of the oxidized dyes by the electrolytes, charge recombination between the oxidised dye molecules and the electrons in the photoanode is o en negligible, and recombination between the electrons in the TiO2 lm and the acceptors in the electrolyte is regarded as the dominant pathway of charge recombination.[4,5,6,7]. The overall efficiency of cells are largely determined by the electron transport and recombination kinetics, and the study of those kinetics in DSSCs is of great signi cance for improving the structure and materials of DSSC photoanodes, the short-circuit current density, and the PCE of cells
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