No abstract

A joint experimental and theoretical study on the stability of dye-sensitized Solar Cells employing a mixture of black dye (N749) and Y1 organic coadsorbent is presented. The aim of the present work is to investigate the stability of these sensitizers, representing the efficiency state of the art in this field. Under the investigated conditions (1100h of ~1Sun light soaking at 55˚C) the co-sensitized device has shown a remarkable stability. The partial desorption of the organic co-adsorbent has been individuated as a possible cause for the slight reduction of the photocurrent value. Theoretical investigations through DFT methods on the dye-sensitized semiconductor surface, revealed a considerably lower adsorption energy for Y1 compared to N749, in particular upon oxidation, possibly leading to the dye desorption under working conditions. Coherently, devices employing only the Y1 organic dye have shown a considerably lower durability.

In the field of functional organic-inorganic hybrid materials, recent trends in the chemistry based on trialkynylorganotins 1 and organically bridged α,ω-bis(trialkynyltin) compounds 2 are reviewed. Compounds 1 reacted with non-porous silica and nanoporous tin dioxide powders to yield hydrophobic, lipophobic or perylene dye-modified oxide materials. The formation of M oxide -O-Sn-C bonds and the release of three molecules of alkyne led to the irreversible chemisorption of 1, the reaction rate and the chain loading depending on the electronic demand and the bulkiness of the organic group grafted. Furthermore, self-assembled tin-based class II hybrid materials were spontaneously formed by hydrolysis of 2 under homogeneous conditions as the two tin atoms were bridged through a rigid or a semi-rigid linker. Subsequent thermal treatment of these hybrids under an oxygen flow at 400-500 • C furnished nanoporous tin dioxide materials consisting of a porous network of aggregated cassiterite tin dioxide particles. An unusual polymodal distribution of mesopore sizes was found in the case of the sample prepared from the hybrid containing the diphenylene spacer.

The surface modification of nanoporous tin dioxide materials was achieved with trialkynylorganotin(IV) (C4H9-C=C)3Sn-(CH2)n(C10H20) (n = 4,6)1 endowed with a perylene dye to yield powders containing up to 0.13 mmol.g-1 of perylene unit or dye-modified thin films. Irreversible chemisorption occurred in solution at room temperature to give perylene dye grafted at the oxide surface via the cleavage of the three tin-alkynide bonds of the precursor and the formation of Snbulk-O-Sn-Cdye linkages. The photoelectrochemical cells made with the 1-modified films demonstrated maximum incident photon to current efficiency (IPCE) as high as 18% at 430 nm under white light illumination. The performances of the cells were interpreted in terms of the intrinsic properties of tin dioxide and aggregation of the perylene dye.