Trap State and Charge Recombination in Nanocrystalline Passivized Conductive and Photoelectrode Interface of Dye-Sensitized Solar Cell

Abstract

The dynamic competition between electron generation and recombination was found to be a bottleneck restricting the development of high-performance dye-sensitized solar cells (DSSCs). Introducing a passivation layer on the surface of the TiO 2 photoelectrode material plays a crucial role in separating the charge by preventing the recombination of photogenerated electrons with the oxidized species. This study aims to understand in detail the kinetics of the electron recombination process of a DSSC fabricated with a conductive substrate and photoelectrode film, both passivized with a layer of nanocrystalline TiO 2 . Interestingly, the coating, which acted as a passivation layer, suppressed the back-electron transfer and improved the overall performance of the integrated DSSC. The passivation layer reduced the exposed site of the fluorine-doped tin oxide (FTO)-electrolyte interface, thereby reducing the dark current phenomenon. In addition, the presence of the passivation layer reduced the rate of electron recombination related to the surface state recombination, as well as the trapping/de-trapping phenomenon. The photovoltaic properties of the nanocrystalline-coated DSSC, such as short-circuit current, open-circuit voltage, and fill factor, showed significant improvement compared to the un-coated photoelectrode film. The overall performance efficiency improved by about 22% compared to the un-coated photoelectrode-based DSSC.The mesoporous oxide photoelectrode material is the heart of a DSSC. It has responsibilities in anchoring the molecules of the dye sensitizer, and it acts as a medium for the transportation of electrons. In recent years, the development of binary and ternary oxide nanostructured photoelectrode materials such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), tin oxide (SnO 2 ), and zinc tin oxide (Zn 2 SnO 4 ) attracted great attention due to their suitable conduction band and unique characteristics for DSC application. As of now, TiO 2 is the semiconductor of choice due to its promising properties such as wide bandgap energy, low cost, abundance, and non-toxic oxides. Moreover, the chemical inertness of TiO 2 makes it possible to allow the dye sensitizer molecule, which commonly has a carboxylate anchoring group, to be attached to the photoelectrode surface. Additionally, other distinguishing features of TiO 2 such as the high relative permittivity of anatase (~30-40) helps in lowering the electrostatic interaction between the injected electrons and oxidized dye molecules, thus reducing the possibilities of electron recombination [5]. Anatase (E g = 3.23 eV), rutile (E g = 3.05 eV), and brookite (E g = 3.26 eV) are three crystalline TiO 2 polymorphs that naturally exist. Brookite with an orthorhombic structure is difficult to synthesize in the laboratory compared to anatase and rutile. Even though rutile and anatase have the same tetragonal structure, a higher Fermi level of anatase by 0.1 eV compared to rutile makes it more desirable for DSSC application [6].When the photosensitized dye receives e...

Influence of the pH of anthocyanins on the efficiency of dye sensitized solar cells

“…The change transfer resistance at the anode and chemical capacitance of anode are related to Eq. (3) through equation (4) and equation (5) respectively [ 38 , 39 ]. …”

“…Using the results of Table 2 ; electron lifetime, ; recombination rate constant, ; constant, Con. And electron charge density, , in the middle of TiO 2 were computed using equations (6) to (9), respectively [ 38 , 39 , 40 , 41 ]. The computed parameters are presented in Table 3 …”

“…However, not all electrons injected in the conduction band contribute to the current. It seems that someelectrons end up in localized states [ 39 , 45 ]. This argument can be supported by examining a graph of chemical capacitance at the anode against applied biasing voltage.…”

Effect of an Aromatic Sulfonate Ligand on the Photovoltaic Performance of Molybdenum Cluster-Sensitized Solar Cells

“…The higher chemical capacitance (Cμ) of the MI-based cells results in the efficient suppression of the trapping/detrapping process of the injected electrons in the CB of TiO 2 . 58 Although NS negatively affects the suppression of the trapping/detrapping process, the MINS 24-based MCSSC shows the fastest electron transport (τ trans ) of 4.2 μs that is faster by 15 times in comparison to MI (τ trans = 64.6 μs). This transfer rate starts to be saturated for the MINS35-based cells (τ trans = 5.7 μs).…”

Improving Ag‐TiO 2 nanocomposites’ current density by TiCl 4 pretreated on FTO glass for dye‐sensitised solar cells

“…From Figure 2(a)we can see that bare FTO grains with irregular shapes ranging from 10 up to a few hundred nm in size were observed in the image. However, in Figure2(b), the image of FTO grains is slightly blurred and a small dot was covered on the grains implying the formation of an extremely thin layer of TiO 2 on the grains[17].To confirm the presence of the TiO 2 thin layer on the FTO grain, energy X-ray dispersive spectroscopy (EDS) was…”