Planar, bulk and hybrid merocyanine/C₆₀heterojunction devices: a case study on thin film morphology and photovoltaic performance

Abstract

The growth of a thermally deposited merocyanine (HB364) thin film can be modified through insertion of a transition metal oxide layer between an indium tin oxide (ITO) covered glass substrate and the dye film. Pure or V 2 O 5 modified ITO substrates result in highly crystalline HB364 films where the dye molecules adopt an edge-on orientation. Changing the transition metal oxide layer to WO 3 or MoO 3 results in a less ordered dye film with a mixed growth of edge-on and face-on orientations. Planar HB364/C 60 heterojunction (PHJ) solar cells are fabricated using the different transition metal oxides as the anode buffer layers. The devices with a pure ITO or a V 2 O 5 modified anode demonstrate the highest power conversion efficiencies up to 2.7% that also outperform HB364:C 60 bulk heterojunction (BHJ) devices (2.5%). Finally, HB364/HB364:C 60 hybrid heterojunction (HHJ) cells are fabricated showing the highest power conversion efficiency of 2.9%.

Impact of Molecular Dipole Moments on Fermi Level Pinning in Thin Films

“…17 The better performance of photovoltaic cells when substituting ITO by a MoO 3 interlayer can readily be understood from our data and can be assigned to E F -pinning at the HOMO of the merocyanine only for very high substrate Φ ox values. For TiO 2 we find large values for the hole injection barrier as well, which means, in turn, low electron injection barriers.…”

Benzochalcogenodiazole‐Based Donor–Acceptor–Acceptor Molecular Donors for Organic Solar Cells

“…This kind of supramolecular arrangement was also observed by Wurthner and Meerholz et al in their study of merocyanine dyes and was proposed to be capable of effectively eliminating molecular dipole moments in the solid state, which thus avoids the large energetic disorder that has an adverse impact on charge-carrier transport. [26][27][28][29][30][31][32] The cyclic voltammograms of these six donor molecules recorded in solution are shown in Figure 2, and the relevant electrochemical data are summarized in Table 1. All molecules showed one quasireversible oxidation wave assigned to the oxidation of the ditolylphenylamine or ditolylthienylamine donor moiety.…”

“…[26][27][28][29][30][31][32][33][34][35] A class of merocyanine dyes with easily tunable optoelectronic properties showed a decent device performance in both solution-and vacuum-processed SMOSCs. [26][27][28][29][30][31][32] Previously, we have reported several molecular Four new molecules with a donor-acceptor-acceptor (D-A-A) configuration, in which 2,1,3-benzoxadiazole or 2,1,3-benzoselenodiazole were adopted as the central bridging acceptor, were synthesized as electron donors for small-molecule organic solar cells. In conjunction with two previously reported 2,1,3benzothiadiazole-based compounds, the influences of the benzochalcogenodiazole acceptor unit and the ditolylarylamine donor moiety on the molecular structure, electrochemical behavior, and optical properties of the materials were investigat-ed systematically to obtain a clear structure-property relationship.…”

Organic Thin Film Transistors Based on Highly Dipolar Donor–Acceptor Polymethine Dyes

“…According to the disorder charge transport theory, it is implied that molecules with a permanent dipole moment will enlarge the density of states (DOS) distribution and thus decrease the charge carrier mobility . On the other hand lots of dipolar molecules have been investigated in the area of nonlinear optics (NLO) and photorefractive (PR) materials, and some showed recently also great promise for organic photovoltaics, first with dye‐sensitized solar cells (DSSCs) and more recently also in bulk and planar heterojunction (BHJ, PHJ) solar cells.…”

“…Here we investigate a large series of merocyanine dyes bearing different electron donor and acceptor heterocycles connected to a dimethine bridge ( Scheme ). The particular choice of these merocyanines was motivated by our earlier work in organic photovoltaics, that is, these merocyanine dyes are all strong absorbers, mostly in the region of largest solar flux, and their HOMO and LUMO levels are well‐matched to fullerene acceptors for PHJ and BHJ solar cells. Accordingly, we could expect that their HOMO level should also be suitable to provide p‐channel transport in OTFTs with gold electrodes at ambient conditions.…”