Snaith group

Abstract:

Diels-Alder reactions of cyclopentadiene to C_2v(19 138)-C₇₆ and YNC@C_2v(19 138)-C₇₆ violating the isolated pentagon rule have been systematically studied by means of density functional theory calculations. As for the free fullerene, the pentalene-type [5,5]-bond in the adjacent pentagon pair is the most favorable from thermodynamic and kinetic viewpoints, which is attributed to the highly strained carbon atoms accompanied by the suitable lowest unoccupied molecular orbital shape with a large distribution to interact with cyclopentadiene. Upon encapsulating the YNC cluster, a corannulene-type [5,6]-bond and a pyracylene-type [6,6]-bond become the two most reactive addition sites under thermodynamic and kinetic conditions, which possess similar reaction energies and energy barriers. Especially, the [5,6]-bond exhibits a larger reaction energy and a lower energy barrier than that on the free fullerene, which should be ascribed to its shorter bond length and larger π-orbital axis vector value after trapping the metallic cluster. The suitable unoccupied molecular orbital lobes with large distributions on the [5,6]- and [6,6]-bonds are also an advantage of cycloadditions. This work presents the first example that the most favorable addition site is remote from the adjacent pentagon pair in the fullerene cage after encapsulating a metallic cluster.

Abstract:

Charge transport layers strongly influence the performance of perovskite solar cells (PSCs). To date, compact layers and mesoporous scaffolds of titanium dioxide have emerged as good electron transport layers (ETL), enabling record power conversion efficiencies (PCE). However, these ETLs require sintering above 400 °C, which excludes them from low-temperature applications such as flexible devices and silicon-heterojunction tandems. Furthermore, instability of TiO2 under prolonged exposure to sunlight appears to be a critical issue. Here, we present the promising characteristics of low-temperature processed strontium titanate (STO) as an ETL to realize PSCs with 19% PCE. STO is a wide bandgap transparent inorganic perovskite. Compared with other low-temperature processed interlayers, STO reduces the parasitic absorption in the ultraviolet and visible range, improves the electron transport, and greatly increases the stability of the devices, retaining ∼80% of their initial efficiency after 1000 h of constant white light illumination.