Engineering Two-Phase and Three-Phase Microstructures from Water-Based Dispersions of Nanoparticles for Eco-Friendly Polymer Solar Cell Applications

Abstract

Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C 61 butyric acid methyl ester (PC 61 BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these singlecomponent particles. Photoluminescence, UV−vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (η ED) of 37% for the two-phase microstructure. The glass transition temperature (T g) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in η ED to 64% due to an increase in donor−acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC 61 BM into amorphous P3HT domains. As such, this study demonstrates the higher level of control over donor−acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.

Printable Organic Semiconductors for Radiation Detection: From Fundamentals to Fabrication and Functionality

“…Controlling OSC material nanoscale morphology across large areas during printing fabrication presents significant challenges using the crude thermodynamic levers of solvent treatments and thermal annealing [83]. One potential avenue to circumvent this challenge is to create discrete nanoparticles from the OSC materials, where the desired morphology is imprinted into the particles through chemically directed assembly using surfactants [84,85]. Such an approach is attractive for two fundamental reasons.…”

“…This emulsion method provides nanoparticulate OSC inks that are stable over time periods of months to years. Nanoparticles of OSCs synthesized via the miniemulsion method encompass various morphologies, including pristine pure semiconductors [84,91,92], core-shell combinations of two semiconductors [23,[93][94][95][96][97], and highly intermixed blends of two semiconductors [8,98]. This morphology has been shown to be tuneable and highly dependent on the relative surface energies of the two materials [99].…”

Manipulating nanoscale structure to control functionality in printed organic photovoltaic, transistor and bioelectronic devices

“…Controlling OE material nanoscale structure and morphology across large areas during printing fabrication remains a significant challenge due to the limited thermodynamic levers discussed previously [156]. One potential avenue to circumvent this challenge is to create discrete nanoparticles where the multi-phase structure is imprinted through chemically directed assembly using sur-factants prior to casting the active films [157,158]. Not only does this approach allow dispersal of the OE nanoparticles into greener solvents such as water and alcohols through the surfaceadsorbed surfactant molecules, it also ensures that the thermodynamic control of film morphology is decoupled from the printing process.…”

“…Not only does this approach allow dispersal of the OE nanoparticles into greener solvents such as water and alcohols through the surfaceadsorbed surfactant molecules, it also ensures that the thermodynamic control of film morphology is decoupled from the printing process. This nanoengineering approach enables the dual benefits of exquisite nanoscale film structure and low cost, large area printing of electronic devices to be Variation of these parameters can systematically create either a core-shell [162][163][164][165][166][167], a pristine [157,168,169], or a molecularly intermixed [170,171] nanoparticle, and can also alter the shape of the particles [172]. This nanoparticulate ink approach offers a unique pathway towards creation of the optimum three phase mat-erial blends composed of pure and intermixed phases, as the charge separation is strongest in the intermolecularly mixed nanoparticles, whereas the charge mobility is much higher in the core-shell and pristine nanoparticles where crystallinity is much higher.…”

Unravelling donor–acceptor film morphology formation for environmentally-friendly OPV ink formulations

“…22,23 To achieve efficient OPV device performance, it is necessary to control the degree of phase separation between the donor and acceptor components. 21,24 The size scale of donor and acceptor domains and the degree of donor-acceptor phase intermixing ( phase purity) have a direct impact on the exciton dissociation efficiency (η ED ), 25 charge carrier mobility, and recombination rates in these systems, 26 all of which directly influence the maximum achievable power conversion efficiency (PCE) of solar cells. It is common to utilise small fractions of co-solvents (additives) to avoid the formation of undesired large circular fullerene domains, during solutionprocessing of OPV, that reduce device performance.…”