Donor–Acceptor Interfaces by Engineered Nanoparticles Assemblies for Enhanced Efficiency in Plastic Planar Heterojunction Solar Cells

Abstract

Precisely positioning functionalized gold nanoparticles assemblies at planar donor−acceptor interfaces results in 14-fold enhancement of power conversion efficiency in P3HT/PCBM organic solar cells on plastic (ITO/PET) substrates. This result has been achieved by employing naphthalenethiol-capped gold nanoparticles (NT-Au-NPs) produced by laser ablation in liquid and size varied in the 10−30 nm range. Upon surface functionalization with the aromatic thiol, these particles self-assemble in submicrometer aggregates, which give increased light scattering. When these aggregates are deposited in the planar heterojunction between the donor and the acceptor systems, the localized scattering leads to a larger exciton formation just in the region of interest for charge transfer.

Synergies and compromises between charge and energy transfers in three-component organic solar cells

“…The thickness of P3HT and PCBM films was maintained at about 50 and 30 nm, respectively by using so-called "orthogonal solvents" (solvents that behave as good solvents for the layer to be deposited but that do not affect the morphology of the polymer below). 10,17 Optical Characterization. UV-Vis absorption and fluorescence spectra were recorded on thin films deposited on PET/ITO substrates, using a Specord S 600 (Analytik Jena, Jena, Germany) and Fluoromax-4 (HORIBA Jobin Yvon, Edison, USA) spectrofluorometer equipped with a 150 W xenon arc lamp as the excitation source, respectively.…”

“…Results are fully in agreement with what previously reported. 17 Under the selected spatiotemporal resolution all the samples are characterized by homogenous average lifetime. X-Rays Photoelectron Spectroscopy.…”

“…Indeed, the ET should induce a fluorescence quenching of F8BT (energy donor) and an increase in fluorescence of P3HT (energy acceptor), but the simultaneous CT from P3HT (electron donor) to F8BT (electron acceptor) would lead to the opposite effect. 17,53,54 However, although the LUMOP3HT-LUMOF8BT offsets is large enough for the exciton dissociation, the charge separation in P3HT/F8BT systems is negligible with respect to the ET (Figures 1a and 1c). 54 In fact, the separation distance between the benzothiadiazole acceptor units in F8BT and the thiophene donor units in P3HT is too long for an efficient exciton dissociation but may be adequate for ET, since the latter is a long range process.…”

“…From the process point of view, realizing a PHJ device would allow easier scalability to large area manufacturing since of a better morphological and structural control than BHJ, which need the appropriate organization of donor and acceptor materials during the spin-coating or the post-production process. [10][11][12][13][14][15][16][17] Moreover, in the PHJs the free charge carriers can benefit from a continuous pathway to the electrodes, contrary to what happens in the BHJs where the presence of a large number of "insulated" domains does not ensure the charge transport. In addition, the PHJ has the further advantage that the donor and acceptor phase contact the anode and the cathode selectively, thus favoring the correct charge extraction.…”

“…In a previous work we have already shown how it is possible to significantly improve ηdiss by using gold nanoparticles able to increase and localize the exciton generation at the donor/acceptor interface in a PHJ. 17 Here, we show how this challenge is also achievable without using expensive materials but by simply incorporating a polymer able to induce an energy transfer (ET) to the electron donor material and, at the same time, to generate a cascade structure. In particular, we demonstrate that it is not sufficient to disperse the third component in the heterojunction, but it is necessary to properly engineer a multilayered structure in order to optimize its effect.…”