Analysis of Charge Transport and Device Performance in Organic Photovoltaic Devices with Active Layers of Self-Assembled Nanospheres

Abstract

Nanoparticle (NP) assemblies are particularly appealing as active layers of organic photovoltaic (OPV) devices because their aqueous synthesis reduces the usage of chlorinated solvents and because the nanoparticle size, ratio, and internal structure can be controlled precisely. Understanding quantitatively the effects of active layer nanostructure on charge carrier transport in NP-assembly-based OPV devices is crucial in order to optimize device performance. Toward this end, in this study, we report results of numerical simulations of electron and hole transport in OPV devices with active layers consisting of P3HT:PCBM nanoparticle assemblies based on deterministic charge carrier transport models. The models account for the dynamics of bounded electron−hole pairs and free charge carriers, as well as trapped charge carrier kinetics, self-consistently with the electric field distribution in the device active layer. The models reproduce both transient photocurrents from time-of-flight (TOF) experiments and steady-state photocurrent density−voltage (J−V) device characteristics from experimental measurements under steady illumination. The simulation results provide quantitative interpretations to the active layer nanostructure effects on charge transport and device power conversion efficiency (PCE). The models also predict improved device PCE by introducing proper interlayers between the active layer and the electrodes and controlling the thickness of the active layer.

Recent advances in the green processing of organic photovoltaic devices from nanoparticle dispersions

“…Such a behavior is in agreement with an increase of the positional disorder in composite NP films. 90 The very same conclusion was made by Han et al 89 They get even one step further, connecting the charge trap-site density to the charge transport pathway lengths. In composite NP films, each NP contains electron-transporting and holetransporting materials, leading to continuous charge transport pathways with shorter charge hopping distances.…”

“…A few publications are devoted to the comparison of the charge carrier transport properties measured by TOF of P3HT:PC 61 BM thin films made either from separate NPs or composite NPs. 68,89 Gehan et al showed the existence of conductive pathways for holes through the bulk for separate as for composite NP films but with clearly more short pathways with low resistance for separate NP films. The TOF hole mobility was slightly lower in separate P3HT:PC 61 BM (1 : 1) NP films (8 Â 10 À5 cm 2 (V s) À1 ) than in pure P3HT NP films (2 Â 10 À4 cm 2 (V s) À1 ) with in both cases a weak dependence with the electric field.…”

Optimization, characterization and upscaling of aqueous solar nanoparticle inks for organic photovoltaics using low-cost donor:acceptor blend

“…Until recently it was speculated that the presence of the applied surfactant was the cause for the reduced efficiency. It has, however, been shown that the actual cause is poor dissociation of excitons generated in the polymer-rich domain [37,38]. This issue has been linked to non-optimal phase-separation within the nanoparticle, which for P3HT:PCBM nanoparticles comprises a core-shell structure with an acceptor-rich core and donorrich shell [23,39].…”

Poly(3-hexylthiophene) Nanoparticles Containing Thiophene-S,S-dioxide: Tuning of Dimensions, Optical and Redox Properties, and Charge Separation under Illumination

“…Indeed, nanoparticles based on conjugated polymers are emerging as multifunctional nanoscale materials that promise great potentials. [27][28][29][30][31][32][33] Here we report that the use of Rozen's reagent, one of the most powerful oxygen transfer agents, [8][9][10][11] allows for the preparation of poly(3-hexylthiophene-S,S-dioxide) nanoparticles, whose properties can be skillfully tuned through the controlled introduction of TDO moieties before or after the formation of poly(3-hexylthiophene) nanoparticles. The different modalities of introduction of TDO moieties causes the formation of either PTDO-NPs obtained from pre-oxygenated P3HT, with dimensions down to 5 nm, or core-shell P3HT@PTDO-NPs obtained from oxygenation of the surface of preformed P3HT nanoparticles.…”