Templating Effects of α-Sexithiophene in Donor–Acceptor Organic Thin Films

Abstract

Small-molecule organic photovoltaic cells often employ a planar heterojunction (PHJ) geometry where the electron donor and acceptor materials are stacked one on top of the other. The thin-film growth scenario of such PHJs can be very different from the one of a single compound on a bare substrate. We have investigated the growth of PHJs, consisting of two different donor−acceptor pairs, namely, α-sexithiophene (6T)/C 60 and 6T/diindenoperylene (DIP) using real-time in situ X-ray scattering. For both donor− acceptor material combinations, we observe that the coherent in-plane crystalline size of the second material strongly correlates with the one of the bottom one, and hence a strong templating effect of the 6T on the material deposited subsequently, indicating a strong interaction between the two materials in the PHJ. Furthermore, a change in the structure of the 6T film during the deposition of the second material was observed, which shows that the deposition of an additional material on top of a templating layer can partially change the crystal structure of the templating film itself.

Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells

“…A fast deposition of α-6T (1 Å/s) on unheated substrate, as employed for the films and HOSCs reported in Figs. 1 and 2 above, results in a mixture of different orientations (standing and lying) with respect to the ITO substrate 46 . In addition, we also prepared films with mainly standing molecules, as well as films containing mainly lying molecules, by employing fabrication parameters which have been used in previous reports (see also ‘Methods’) 46 – 48 .…”

“…1 and 2 above, results in a mixture of different orientations (standing and lying) with respect to the ITO substrate 46 . In addition, we also prepared films with mainly standing molecules, as well as films containing mainly lying molecules, by employing fabrication parameters which have been used in previous reports (see also ‘Methods’) 46 – 48 . In the lying orientation, the absorbance is maximised due to the parallel alignment between the transition dipole moment of the molecule and the electric field vector of incident light (Fig.…”

Efficiency enhancement of small molecule organic solar cells using hexapropyltruxene as an interface layer

“…A significant consequence of the insertion of interlayers is the change in morphology introduced by its template effect. Such a template layer thus can be used to influence the molecular ordering to increase the PCE of OSCs because the ordering of the molecules in the photovoltaic active layer of an OSC can have profound consequences on their performance [26][27][28][29] , including improved absorption and more efficient exciton and charge carrier transport 26,[30][31][32] . Furthermore, the energy levels of the electrode materials can also be modified by the template layer 27,33,34 , which is important for device performance 33 .…”

Fast fitting of reflectivity data of growing thin films using neural networks

“…For the performance evaluation on the experimental data, the film properties determined by the model were compared with a manual LMS fit using a genetic algorithm (GenX). The studied systems were two DIP films, one CuPc film and one 6T film, each grown at 303 K, as well a third DIP film, grown at 403 K. Three out of five of these data sets have already been analyzed and published [DIP 303 K (Hinderhofer et al, 2010), DIP 403 K (Kowarik et al, 2006) and 6T (Lorch et al, 2015)]. Fitting performance of the neural network model on a DIP film grown at 303 K with a deposition rate of 1 Å min À1 .…”