Tailoring Nanoscale Morphology of Polymer:Fullerene Blends Using Electrostatic Field

Abstract

To tailor the nanomorphology in polymer/fullerene blends, we study the effect of electrostatic field (E-field) on the solidification of poly(3-hexylthiophene-2, 5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ). In addition to control; wet P3HT:PCBM thin films were exposed to E-field of Van de Graaff (VDG) generator at three different directions-horizontal (H), tilted (T), and vertical (V)-relative to the plane of the substrate. Surface and bulk characterizations of the field-treated BHJs affirmed that fullerene molecules can easily penetrate the spaghetti-like P3HT and move up and down following the E-field. Using E-field treatment, we achieved favorable morphologies with efficient charge separation, transport, and collection. We improve; (1) the hole mobility values up to 19.4 × 10 ± 1.6 × 10 cm V s and (2) the power conversion efficiency (PCE) of conventional and inverted OPVs up to 2.58 ± 0.02% and 4.1 ± 0.40%, respectively. This E-field approach can serve as a new morphology-tuning technique, which is generally applicable to other polymer-fullerene systems.

Effect of Ag2S nanoparticles on optical, photophysical, and electrical properties of P3HT thin films

“…[ 8 ] The shorter lifetime, that is τ 1 with relative integrated intensities B 1 = 84% corresponded to the decay of first singlet state, [ 44 ] whereas the delayed decay τ 2 with relative integrated intensity B 2 = 16% was associated with the emission of vibrational electronic states due to coupling between an electronic state and phonon modes of the first singlet state. [ 45 ] It can be noted from Table 1 that both τ 1 , and τ 2 decreased with increase in Ag 2 S content up to the ratio P3HT1:1.6 with τ 1 = 84 ps and τ 2 = 326 ps, and thereafter slightly increased for higher Ag 2 S content. The average lifetime (τ avg ) was evaluated using the relationship 8 :…”

Origin of Hole Transport in Small Molecule Dilute Donor Solar Cells

“…Recently, single-junction organic solar cells (OSCs) reached remarkable power conversion efficiencies (PCEs) of 18%, [1][2][3] facilitated by the usage of novel materials, especially nonfullerene acceptors, [4,5] and increased control of film morphologies. [6][7][8] Understanding the generation of free charge carriers from absorbed photons is fundamental to design novel organic semiconductors and to tailor the electronic properties of interfaces in donor:acceptor blends for efficient solar cells. Despite the rapid increase in efficiencies, we are still lacking a detailed understanding of the motion of photogenerated charge carriers within the multiphase thin films consisting of crystalline and amorphous domains, or even strongly mixed donor: acceptor phases.…”

“…In contrast to previous kMC studies, the driving force for exciton dissociation is accounted for. As a study system, nitrogenbridged terthiophene (NBTT) molecules in a [6,6]-phenyl-C70-butyric acid methyl ester (PC 71 BM) matrix are investigated. The simulations show that hole back transfer from the small molecule donor to the fullerene matrix explains the measured concentration dependences of the photocurrents as well as the J sc dependence on the light intensity for donor concentrations below 5 wt%.…”

“…Donor aggregation to form percolation pathways was shown for donor concentrations larger than 5 wt% from simulated deposition using classical molecular dynamics [21] and above 10 vol% from Kelvin Probe Force Microscopy. [22] Hole back transfer from isolated donor molecules to the fullerene matrix was proposed as an alternative mechanism for the sufficient generation of photocurrent in dilute donor poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C70-butyric acid methyl ester (PC 71 BM) solar cells. [23] Back transfer is enabled by an effective barrier lowering induced by two mechanisms: 1) the highest occupied molecular orbital (HOMO) energies of isolated P3HT chains in the PC 71 BM matrix are shifted toward the HOMO level of PC 71 BM, and 2) Coulomb repulsion of trapped holes on the P3HT chains leads to an efficient back transfer.…”

A Genetic Algorithm Approach to Design Principles for Organic Photovoltaic Materials

“…For instance, a donor excited molecule with an energy level higher than that of an adjacent acceptor favors the dissociation of excitons by means of electron transfers to the acceptor. The importance of such pairing of energy levels has also been shown to relate to the open circuit voltage and thus to the overall efficiency of the photovoltaic cell [16] .Furthermore, morphology plays a vital role in the efficiency of charge transfer and efforts regarding morphology tuning have been undertaken by several means including reducing surface roughness [17] , application of electric fields [18] , different choices of solvents and additives [19,20,21] and molecular engineering [22,23] When it comes to modeling the various phenomena involved in the working of an OPV device, many studies have focused on each individual process at play.…”