a cheap and scalable approach that is also the main strength of alternative technologies such as organic photovoltaics, dye-sensitized solar cells and colloidal quantum dot-based solar cells.
By time-resolved transient photoluminescence, 2 papers (published at the same time) claimed extremely high carrier diffusion lengths of > 100 nm. In one of the papers, the mixed halide perovskite has an even longer diffusion length of >1000 nm. charge-carrier extraction model based on diffusion was used to estimate the charge carrier diffusion lengths, obtained minimum estimates of 130 and 90 nm for electrons and holes, respectively. (compared to the only 10 nm for polymers in PV.)
Coupled/correlated electron-hole pairs. Conventional solar cells, such as silicon p-n junction, photogeneration of free electron-hole pairs occurs throughout the bulk semiconductor in conventional cells. Excitonic solar cells, such as OPV and DSSC, consists of cells in which light absorption results in the production of a transiently localized excited state that cannot thermally dissociate (binding energy ≫ kT). In other words, the absorbed photon produces a neutral excitation, not free carriers. Therefore, a dissociation interface is required.
and colleagues were working on photovoltaics called dye-sensitized solar cells (DSSCs). Unlike conventional silicon solar cells, DSSCs consist of a blend of organic light-absorbing dyes coating tiny inorganic particles such as titanium dioxide (TiO2), which in turn are surrounded by a charge-conducting electrolyte. In standard DSSCs, when a dye molecule absorbs a photon, the light boosts the energy of one of the electrons in the dye, enabling it to jump onto a TiO2 particle. From there, it skips from particle to particle until it reaches an electrode, where it’s collected and sent through a circuit to do work. Meanwhile, another electron jumps from the electrolyte to the dye to restore it to its original state.
He says that it took one of his students 2 years to find a recipe to make the material sturdy enough for a brief demonstration.
DSSC are considered to be ‘excitonic’ photovoltaics that require a large surface area for charge separation between electron-accepting TiO2 and the adsorbed dye layer.
Either a solution of the organic and inorganic materials is used to create the film or the two components are thermally evaporated together inside a vacuum chamber.