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Reducing the spatial inhomogeneity of solution-processed, multicrystalline methylammonium lead iodide (MAPbI3) perovskite is of great importance for improving its power conversion efficiency, suppressing point-to-point deviations, and delaying degradation during operation. Various techniques, such as conducting-mode atomic force microscopy and photoluminescence mapping, have been applied for this intriguing class of materials, revealing nonuniform electronic properties on the nanometer-to-micrometer scale. Here, we designed a new space- and time-resolved microwave conductivity system that enables mapping of the transient photoconductivity with resolution greater than ∼45 μm. We examined the effects of the precursor concentration of MAPbI3 and the mixing of halides (I– and Br–) on the charge carrier dynamics, crystal size, and inhomogeneity of the films. The optoelectronic inhomogeneity of MAPbI3 and MAPb(I1–xBrx)3 on the sub-millimeter and millimeter scales shows a general correlation with their crystallite sizes, whereas the precursor concentration and halide mixing affect the inhomogeneity in a different way, providing a basis for uniform processing of a multicrystalline perovskite film.

Interest in ternary blend organic photovoltaics (OPVs) has been triggered by improved power conversion efficiency (PCE), simple fabrication, and a variety of material combinations. They typically consist of a p-type donor, an n-type fullerene, and a secondary p-type donor, where the two donors undergo complementary photoabsorption to increase the photocurrent. In contrast to this general strategy, we have incorporated propeller-shaped, high-bandgap triptycene (TP) into a bulk heterojunction (BHJ) composed of a conjugated polymer (P3HT, PTB7, and PffBT4T) and methano[60]fullerene (PCBM). The TP molecules self-organize into two-dimensional (2D) layers. Based on their energy levels, these layers are not expected to trap charge carriers. The performance of these OPV devices is discussed in conjunction with film morphology, transient photoconductivity, mobility, crystalline structure, and surface free energy. Herein, we demonstrate that the PCE of the crystalline polymer (PffBT4T):PCBM with 5 wt% TP is slightly improved (maximum: 9.41%, average: 8.96 ± 0.23%) without the use of a solvent additive, along with much enhanced long-term stability. This is presumably due to the presence of the TP sheet that acts as a nucleation agent and facilitates the crystallization of the polymer. The features of the TP scaffold give rise to a high-performance, additive-free ternary BHJ. Thus, further exploration through chemical functionalization of TP is warranted.

Continuous tuning of the backbone conformation and interchain distance of a π-conjugated polymer is an essential prerequisite to unveil the inherent electrical and optical features of organic electronics. To this end, applying pressure in a hydrostatic medium or diamond anvil cell is a facile approach without the need for side-chain synthetic engineering. We report the development of high-pressure, time-resolved microwave conductivity (HP-TRMC) and evaluation of transient photoconductivity in the regioregular poly(3-hexylthiophene) (P3HT) film and its bulk heterojunction blend with methanofullerene (PCBM). X-ray diffraction experiments under high pressure were performed to detail the pressure dependence of π-stacking and interlamellar distances in P3HT crystallites and PCBM aggregates. The HP-TRMC results were further correlated with high-pressure Raman spectroscopy and density functional theory calculation. The increased HP-TRMC conductivity of P3HT under pressure was found to be relevant to the planarity of the backbone conformation and intramolecular hole mobility. The effects of pressure on the backbone planarity are estimated to be ∼0.3 kJ mol(-1) based on the compressibility derived from the X-ray diffraction under high pressure, suggesting the high enough energy to cause modulation of the planarity in terms of the Landau-de Gennes free energy of isolated P3HT chains as 0.23 kJ mol(-1). In contrast, the P3HT:PCBM blend showed a simple decrease in photoconductivity irrespective of the identical compressive behavior of P3HT. A mechanistic insight into the interplay of intra- and intermolecular mobilities is a key to tailoring the dynamic π-figuration associated with electrical properties, which may lead to the use of HP-TRMC for exploring divergent π-conjugated materials at the desired molecular arrangement and conformation.