The Role of Order in the Amplification of Light‐Energy Conversion in a Dye‐Sensitized Solar Cell Coupled to a Photonic Crystal

We investigate the cause of amplification of light‐energy conversion when coupling a nc‐TiO₂ film to a TiO₂ inverse opal by comparing it to an inverse TiO₂ glass (i‐TiO₂‐g) fabricated with the exact monodisperse air–hole size as an inverse opal with a stop band at 600 nm (600‐i‐TiO₂‐o). A significant twofold average gain in the photon‐to‐current conversion efficiency is measured to the red of the stop band at the 600‐i‐TiO₂‐o/nc‐TiO₂ bilayer under front‐wall and back‐wall illumination, greater than the gain within the stop band. A smaller amplification is measured under front‐wall illumination—and no gain is measured under back‐wall illumination—for i‐TiO₂‐g/nc‐TiO₂ at these energies. The photonic crystal therefore causes trapping of light through the bilayer, not only within the gap but also to the red, at frequencies within its dielectric band. This light‐trapping effect is found to be dependent on structural order, as a highly disordered inverse glass film with the same air–hole size and thickness does not yield the same gain. A drop in the transmission of light is measured within the same frequencies to the red of the stop band upon adding nc‐TiO₂ to 600‐i‐TiO₂‐o, consistent with light trapping in the bilayer.     

Kinetics and mechanism of the oxidation of a ternary complex involving nitrilotriacetatocobaltate(II) and malonic acid by N-bromosuccinimide

The kinetics of oxidation of [Co^IINM(H₂O)]^3– (N = nitrilotriacetate, M = malonate) by N-bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: d[Co^III]/dt = k ₁ K ₂[NBS][Co^II]_T/{1 + K₂[NBS] + (H⁺/K₁)} where k ₁ is the rate constant for the electron transfer process, K ₁ the equilibrium constant for dissociation of [Co^IINM(H₂O)]^3– to [Co^IINM(OH)]^4– + H⁺, and K ₂ the pre-equilibrium formation constant. Values of k ₁ = 1.07 × 10^–3 s^–1, K ₁ = 4.74 × 10^–8 mol dm^–3 and K ₂ = 472 dm³ mol^–1 have been obtained at 30 °C and I = 0.2 mol dm^–3. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Co^IINM(OH)]^4– is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.