Muhammad Imran Asghar

Rediscovering a Key Interface in Dye-Sensitized Solar Cells: Guanidinium and Iodine Competition for Binding Sites at the Dye/Electrolyte Surface

We propose a new mechanism by which the common electrolyte additive guanidinium thiocyanate (GdmSCN) improves efficiency in dye-sensitized solar cells (DSSCs). We demonstrate that binding of Gdm(+) to TiO2 is weak and does not passivate recombination sites on the TiO2 surface as has been previously claimed. Instead, we show that Gdm(+) binds strongly to the N719 and D131 dyes and probably to many similar compounds. The binding of Gdm(+) competes with iodine binding to the same molecule, reducing the surface concentration of dye-I2 complexes. This in turn reduces the electron/iodine recombination rate constant, which increases the collection efficiency and thus the photocurrent. We further observe that GdmNO3 can increase efficiency more than the current Gdm(+) source, GdmSCN, at least in some DSSCs. Overall, the results point to an improved paradigm for DSSC operation and development. The TiO2/electrolyte surface has long been held to be the key interface in DSSCs. We now assert that the dye layer/electrolyte interaction is at least, and probably more, important.

Modeling boron diffusion gettering of iron in silicon solar cells

In this paper, a model is presented for boron diffusion gettering of iron in silicon during thermal processing. In the model, both the segregation of iron due to high boron doping concentration and heterogeneous precipitation of iron to the surface of the wafer are taken into account. It is shown, by comparing simulated results with experimental ones, that this model can be used to estimate boron diffusion gettering efficiency of iron under a variety of processing conditions. Finally, the application of the model to phosphorus diffusion gettering is discussed.

Comparative analysis of ceramic-carbonate nanocomposite fuel cells using composite GDC/NLC electrolyte with different perovskite structured cathode materials

A comparative analysis of perovskite structured cathode materials, La0.65Sr0.35MnO3 (LSM), La0.8Sr0.2CoO3 (LSC), La0.6Sr0.4FeO3 (LSF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was performed for a ceramic-carbonate nanocomposite fuel cell using composite electrolyte consisting of Gd0.1Ce0.9O1.95 (GDC) and a eutectic mixture of Na2CO3 and Li2CO3. The compatibility of these nanocomposite electrode powder materials was investigated under air, CO2 and air/CO2 atmospheres at 550 °C. Microscopy measurements together with energy dispersive X-ray spectroscopy (EDS) elementary analysis revealed few spots with higher counts of manganese relative to lanthanum and strontium under pure CO2 atmosphere. Furthermore, electrochemical impedance (EIS) analysis showed that LSC had the lowest resistance to oxygen reduction reaction (ORR) (14.12 Ω∙cm2) followed by LSF (15.23 Ω∙cm2), LSCF (19.38 Ω∙cm2) and LSM (>300 Ω∙cm2). In addition, low frequency EIS measurements (down to 50 μHz) revealed two additional semi-circles at frequencies around 1 Hz. These semicircles can yield additional information about electrochemical reactions in the device. Finally, a fuel cell was fabricated using GDC/NLC nanocomposite electrolyte and its composite with NiO and LSCF as anode and cathode, respectively. The cell produced an excellent power density of 1.06 W/cm2 at 550 °C under fuel cell conditions.