This work reports on a synthetic strategy to generate poly(3-alkylthiophene)s (P3ATs) with jointsimultaneous control of the molar mass and the regioregularity. A series of chiral P3ATswith different regioregularities is synthesized using a Pd(RuPhos)-catalyzed chain-growth polymerisation. All polymers have molar masses and polydispersities (PDI) that lie within a narrow region. Furthermore, it is shown that the Pd-catalyst forms all kinds of couplings [head-to-tail (HT), tail-to-tail (TT) and head-to-head (HH)] to a similar extent, which allows to insert predictable amounts of regio-irregularities into the polymer chain. This enables a thorough study of the influence of the regioregularity on the properties of P3AT, which was performed using UV-vis and circular dichroïsm (CD) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy (AFM) measurements. Unexpectedly, it is found that in "kinetic" conditions the highest crystallinity, π-stacking, supramolecular organisation and chiral expression are not obtained for fully regioregular P3AT with 100% HT couplings, but that a small amount of regio-irregularity increases these properties and the chiral expression. In "thermodynamical" conditions (after annealing, very slow solvent evaporation or very slow cooling from the melt), this effect is less pronounced or not found. This behaviour can be explained by a higher degree of motional freedom within the non-perfect polymer chains due to the increased steric repulsion from the HH-couplings, which leads to a more easy stacking in "kinetic" conditions.

We use high-resolution, spatially resolved, laser beam induced current, confocal photoluminescence, and photoconductive atomic force microscopy (pcAFM) measurements to correlate local solar cell performance with spatially heterogeneous local material properties in methylammonium lead triiodide (CHNHPbI) perovskite solar cells. We find that, for this material and device architecture, the photocurrent heterogeneity measured via pcAFM on devices missing a top selective contact with traditional Au-coated tips is significantly larger than the photocurrent heterogeneity observed in full devices with both electron- and hole-selective extraction layers, indicating that extraction barriers at the Au/perovskite interface are ameliorated by deposition of the organic charge extraction layer. Nevertheless, in completed, efficient device structures (PCE ≈ 16%) with state-of-the-art nickel oxide and [6,6]-phenyl-C61-butyric acid (PCBM) methyl ester contacts, we observe that the local photoluminescence (PL) is weakly anticorrelated with local photocurrent at both short-circuit and open-circuit conditions. We determine that the contact materials are fairly homogeneous; thus the heterogeneity stems from the perovskite itself. We suggest a cause for the anticorrelation as being related to local carrier extraction heterogeneity. However, we find that the contacts are still the dominating source of losses in these devices, which minimizes the impact of the material heterogeneity on device performance at present. These results suggest that further steps to prevent recombination losses at the interfaces are needed to help perovskite-based cells approach theoretical efficiency limits; only at this point will material heterogeneity become crucial.

We conduct correlated laser scanning confocal photoluminescence (PL) microscopy, scanning kelvin probe microscopy, and conductive atomic force microscopy (c-AFM) to understand the origins and effects of local heterogeneity in films of the hybrid organic–inorganic perovskite semiconductor methylammonium lead tribromide (MAPbBr3). We compare PL between perovskite films deposited on glass and on hole-transporting contacts. In both systems, we observe heterogeneous PL, but this heterogeneity is due to different mechanisms. On glass substrates, we observe that the PL maps are dominated by lateral carrier diffusion, and on hole-transporting contacts, we observe an anticorrelation between PL and local hole injected current as measured by c-AFM. We conclude that the local variations are due to heterogeneous electronic coupling at the perovskite–electrode interface. We also show that correlated PL and AFM studies are expected to play a key role in studying the electronic heterogeneities in the perovskite itself, which are currently screened by the perovskite–contact interfaces. Our results suggest the need for new selective contacts to improve the charge transfer at the perovskite–contact interfaces.

In this work, methylammonium lead tribromide (MAPbBr3) single crystals are studied by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). We demonstrate that the surface photovoltage and crystal photostriction can be simultaneously investigated by implementing a specific protocol based on the acquisition of the tip height and surface potential during illumination sequences. The obtained data confirm the existence of lattice expansion under illumination in MAPbBr3 and that negative photocarriers accumulate near the crystal surface due to band bending effects. Time-dependent changes of the surface potential occurring under illumination on the scale of a few seconds reveal the existence of slow ion-migration mechanisms. Lastly, photopotential decay at the sub-millisecond time scale related to the photocarrier lifetime is quantified by performing KPFM measurements under frequency-modulated illumination. Our multimodal approach provides a unique way to investigate the interplay between the charges and ionic species, the photocarrier-lattice coupling and the photocarrier dynamics in hybrid perovskites.