Self-doping is a particular doping method that has been applied to a wide range of organic semiconductors. However, there is a lack of understanding regarding the relationship between dopant structure and function. A structurally diverse series of self-n-doped perylene diimides (PDIs) is investigated to study the impact of steric encumbrance, counterion selection, and dopant/PDI tether distance on functional parameters such as doping, stability, morphology, and charge-carrier mobility. The studies show that self-n-doping is best enabled by the use of sterically encumbered ammoniums with short tethers and Lewis basic counterions. Additionally, water is found to inhibit doping, which concludes that thermal degradation is merely a phenomenological feature of certain dopants, and that residual solvent evaporation is the primary driver of thermally activated doping. In situ grazing-incidence wide-angle X-ray scattering studies show that sample annealing increases the π-π stacking distance and shrinks grain boundaries for improved long-range ordering. These features are then correlated to contactless carrier-mobility measurements with time-resolved microwave conductivity before and after thermal annealing. The collective relationships between structural features and functionality are finally used to establish explicit self-n-dopant design principles for the future design of materials with improved functionality.

The development of Sn-based metal halide perovskites (MHP) for thermoelectric applications along with many other device applications has thus far been limited by self-doping degradation and ion migration. Each of these effects decreases the electronic stability and prevents Sn MHPs from performing at their full potential. Motivated by the hypothesis that a pi-conjugated crosslinking agent may fill or block halide vacancies that would otherwise be oxygen-doped, we sought to perform a detailed study of the morphological and electronic degradation of Sn MHPs when 3-aminophenyl boronic acid (3APBA) is introduced. The level of p-type self-doping in Sn MHPs was modified by controlling the ratio of pi-conjugated crosslinking agent to Sn MHP in solution, which significantly impacts the electronic structure and thermoelectric properties of Sn MHPs. Additionally, these findings suggest that the incorporation of crosslinking agents can limit voltage bias stress effects caused by ion migration, which could be applied to a broad range of MHP materials that experience internal instabilities due to ionic effects.

The demand for multifunctional devices continues to drive the evolution and parametrization of technology. Simultaneously, the breadth of structural, morphological, and electronic information that can be used to study materials widens and grows in complexity. To keep up with the demand for superior technologies in disparate fields, such as energy, electronics, and biotechnology, an unparalleled amount of manpower and financial resources have been devoted to the development of materials that can integrate multiple functionalities, particularly functions that ostensibly exclude one another. To address different functionalities at once, materials have become highly complex and often exhibit multiple structural and morphological phases, hierarchical dependencies, and far-from-equilibrium dynamic structures with little to no long-range atomic ordering. A major area of study that is quickly evolving deals with the quantitative characterization of structure-property-function relationships in complex materials based on pi-conjugated organic and organometal systems-particularly in thin film formulations. In this review, we discuss various research avenues where cleverly engineered self-assembly protocols, as well as characterization methods for probing morphology and electronic structure, are implemented to enable the fabrication of well-defined emergent materials.

To close the technological gap between laboratory-based conducting polymers and commercially available inorganic semiconductors, it is imperative to develop synthesis approaches that allow for the fabrication of morphology-controlled polymers where charge carriers can be readily fine-tuned. Herein, our studies provide a detailed investigation of the polymerization protocols needed to afford the fabrication of well-defined and highly ordered polymer thin films. Using poly(3,4-ethylenedioxythiophene (PEDOT) as a case study, we demonstrate strong correlations between the polymerization protocols and counterion dopants in driving the observed changes in crystallinity and pi-stacking ordering of fabricated thin films. Upon the fabrication of thin films with controlled morphologies, we can provide an in-depth characterization of the thermoelectric properties (i.e., electrical conductivity, Seebeck coefficient, and power factor) of doped PEDOT chains as a function of counterion dopants and oxidation levels. Given the high power factors, we fit the thermoelectric characteristics of our samples to determine the charge transport mechanism in PEDOT thin films as a function of polymerization protocols and counterion dopants. On the basis of the fits, we report record-breaking transport function values which are indicative of bandlike transport in PEDOT thin films. As such, these high transport function values may point to the fabrication of well-defined and highly conducting polymers that can achieve thermoelectric figure of merit values above 0.6 at room temperature.

Two‐dimensional coordination polymers (2DCPs) have been predicted to exhibit exotic properties such as superconductivity, topological insulating behavior, catalytic activity, and superior ion transport for energy applications; experimentally, these materials have fallen short of their expectation due to the lack of synthesis protocols that yield continuous, large crystallite domains, and highly ordered thin films with controllable physical and chemical properties. Herein, the fabrication of large‐area, highly ordered 2DCP thin films with large crystallite domains using chemical vapor deposition (CVD) approaches is described. It is demonstrated that defects and the packing motifs of 2DCP thin films may be controlled by adjusting the vapor–vapor and vapor–solid interactions of the metal and organic linker precursors during the CVD fabrication process. Such control allows for the fabrication of defects‐controlled 2DCP thin films that show either semiconducting or metallic behavior. The findings provide the first demonstration of tuning the electrical properties of sub 100 nm‐thick continuous 2DCP thin films by controlling their electronic landscape through defect engineering. As such, it is determined that large‐area, highly ordered 2DCP thin films may undergo a semiconducting to metallic transition that is correlated to changes in morphology, crystalline domain sizes, crystallite orientation, defect interactions, and electronic structure.

We determined how morphology, electronic and interfacial interactions affect perovskite PVs under voltage bias stress. Our findings provide insights into the discrepancies in the solar cell efficiencies observed across many different research groups.

We provide fundamental design principles on the effect of dopant structure (steric hindrance) on the doping efficiency in highly oriented self-doped organic semiconducting thin films.

In this work, we report on the growth of high-mobility β-Ga2O3 homoepitaxial thin films grown at a temperature much lower than the conventional growth temperature window for metalorganic vapor phase epitaxy. Low-temperature β-Ga2O3 thin films grown at 600 °C on Fe-doped (010) bulk substrates exhibit remarkable crystalline quality, which is evident from the measured room temperature Hall mobility of 186 cm2/V s for the unintentionally doped films. N-type doping is achieved by using Si as a dopant, and a controllable doping in the range of 2 × 1016–2 × 1019 cm−3 is studied. Si incorporation and activation is studied by comparing the silicon concentration from secondary ion mass spectroscopy and the electron concentration from temperature-dependent Hall measurements. The films exhibit high purity (low C and H concentrations) with a very low concentration of compensating acceptors (2 × 1015 cm−3) even at this growth temperature. Additionally, an abrupt doping profile with a forward decay of ∼ 5 nm/dec (10 times improvement compared to what is observed for thin films grown at 810 °C) is demonstrated by growing at a lower temperature.

AbstractMethylammonium lead halide perovskite‐based solar cells have demonstrated efficiencies as high as 24.2 %, highlighting their potential as inexpensive and solution‐processable alternatives to silicon solar cell technologies. Poor stability towards moisture, ultraviolet irradiation, heat, and a bias voltage of the perovskite layer and its various device interfaces limits the commercial feasibility of this material for outdoor applications. Herein, we investigate the role of hydrogen bonding interactions induced when metal halide perovskite crystals are crosslinked with alkyl or π‐conjugated boronic acid small molecules (‐B(OH)2). The crosslinked perovskite crystals are investigated under continuous light irradiation and moisture exposure. These studies demonstrate that the origin of the interaction between the alkyl or π‐conjugated crosslinking molecules is due to hydrogen bonding between the ‐B(OH)2 terminal group of the crosslinker and the I of the [PbI6]4− octahedra of the perovskite layer. Also, this interaction influences the stability of the perovskite layer towards moisture and ultraviolet light irradiation. Morphology and structural analyses, as well as IR studies as a function of aging under both dark and light conditions show that π‐conjugated boronic acid molecules are more effective crosslinkers of the perovskite crystals than their alkyl counterparts thus imparting better stability towards light and moisture degradation.

Thin film materials have become increasingly complex in morphological and structural design. When characterizing the structure of these films, a crucial field of study is the role that crystallite orientation plays in giving rise to unique electronic properties. It is therefore important to have a comparative tool for understanding differences in crystallite orientation within a thin film, and also the ability to compare the structural orientation between different thin films. Herein, we designed a new method dubbed the mosaicity factor (MF) to quantify crystallite orientation in thin films using grazing incidence wide-angle X-ray scattering (GIWAXS) patterns. This method for quantifying the orientation of thin films overcomes many limitations inherent in previous approaches such as noise sensitivity, the ability to compare orientation distributions along different axes, and the ability to quantify multiple crystallite orientations observed within the same Miller index. Following the presentation of MF, we proceed to discussing case studies to show the efficacy and range of application available for the use of MF. These studies show how using the MF approach yields quantitative orientation information for various materials assembled on a substrate.

Large size cation (PA) was introduced into the grain boundary and film surface of the 3D perovskite to improve the solar cell efficiency and moisture stability.

Perovskites based on methylammonium lead halides, CH3NH3PbX3 (X = Cl, Br, I), have emerged as one of the most promising materials in solar cell technology. Although the photovoltaics field has witnessed significant progress in the power conversion efficiency (PCE) of perovskite solar cells, unveiling the contribution of the various factors (i.e., energy level alignment, trap states, electron (hole) mobility, interface interactions, and morphology) affecting the observed PCEs is extremely crucial to achieve reproducible and stable devices. This work aims to understand charge transport and recombination within conventional perovskite solar cells due to modifications of the morphology, optoelectronic properties, and energy levels of the titania electron transport layer. Here, we utilize two different processing methods (i.e., solution and sputtering depositions) to yield three morphologically different titania electron transport layers (i.e., planar bulk TiO2, mesoporous TiOx, and sputtered TiO2). We find that the most important factors affecting the PCEs in perovskite solar cells are related to trap-assisted recombination and energy level alignment due to variations in the electron transport layer/perovskite interface. Similarly, we observe that morphologies of both the electron transport layer and the perovskite active layer play a minor role on the observed PCEs.

Nanowire arrays of SnS/SnS2 p–n heterojunctions are grown on transparent indium tin oxide (ITO) coated-glass and Si/SiO2 substrates via chemical vapor transport (CVT). The nanowire arrays are comprised of individual SnS/SnS2 heterostructures that are highly oriented with their lengths and morphologies controlled by the CVT conditions (i.e. reaction temperature, flow rate, and reaction time). The growth and optoelectronic characterization of these well-defined SnS/SnS2 p–n heterostructures pave the way for the fabrication of highly efficient solar cell devices.