Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.

Reversible photo-induced performance deterioration is observed in mesoporous TiO 2 -containing devices in an inert environment. This phenomenon is correlated with the activation of deep trap sites due to astoichiometry of the metal oxide. Interestingly, in air, these defects can be passivated by oxygen adsorption. These results show that the doping of TiO 2 with aluminium has a striking impact upon the density of sub-gap states and enhances the conductivity by orders of magnitude. Dye-sensitized and perovskite solar cells employing Al-doped TiO 2 have increased device effi ciencies and signifi cantly enhanced operational device stability in inert atmospheres. This performance and stability enhancement is attributed to the substitutional incorporation of Al in the anatase lattice, "permanently" passivating electronic trap sites in the bulk and at the surface of the TiO 2 .

The miscibility and aggregation of PCBM ([6,6]-phenyl-C 61 -butyric acid methyl ester) in a polymer matrix is of great importance for the development of fullerene-based organic photovoltaic cells (OPVs). In this study we have systematically investigated the loading of PCBM in regioregular and regiorandom P3HT (poly(3-hexylthiophene-2,5-diyl). Using optical microscopy, we demonstrate the partial miscibility of PCBM in thermally annealed P3HT films and relate it to the relative crystallinity of P3HT. The low polydispersity and the nearly 100% regioregularity of a self-synthesized P3HT allowed a detailed X-ray characterization as a function of PCBM content, revealing a superstructure of periodic amorphous and crystalline lamellar domains of fully chain extended polymer chains. PCBM dissolves in the amorphous interlamellar P3HT regions (partially indexmatching the X-ray scattering contrast) up to a threshold, above which PCBM aggregates start to form. These results show that crystallization of P3HT into 10-nm-wide lamellar domains sets the main length scale in P3HT/PCBM structure formation. PCBM is displaced into the amorphous intralamellar regions, swelling the lamellar stack. This structure formation by crystallization, which is intrinsic to most semicrystalline polymers, followed by the enrichment, segregation, and crystallization of PCBM provides an interdigitated structure, which is conceptually ideal for excitonic solar cells.

Recently, solution-processable organic-inorganic metal halide perovskites have come to the fore as a result of their high power-conversion efficiencies (PCE) in photovoltaics, exceeding 17%. To attain reproducibility in the performance, one of the critical factors is the processing conditions of the perovskite film, which directly influences the photophysical properties and hence the device performance. Here we study the effect of annealing parameters on the crystal structure of the perovskite films and correlate these changes with its photophysical properties. We find that the crystal formation is kinetically driven by the annealing atmosphere, time and temperature. Annealing in air produces an improved crystallinity and large grain domains as compared to nitrogen. Lower photoluminescence quantum efficiency (PLQE) and shorter photoluminescence (PL) lifetimes are observed for nitrogen annealed perovskite films as compared to the air-annealed counterparts. We note that the limiting nonradiative pathways (i.e., maximizing PLQE) is important for obtaining the highest device efficiency. This indicates a critical impact of the atmosphere upon crystallization and the ultimate device performance.