Comparing the backfilling of mesoporous titania thin films with hole conductors of different sizes sharing the same mass density

• Main Authors: Raphael S. Märkl, Nuri Hohn, Emanuel Hupf, Lorenz Bießmann, Volker Körstgens, Lucas P. Kreuzer, Gaetano Mangiapia, Matthias Pomm, Armin Kriele, Eric Rivard, Peter Müller-Buschbaum
• Format: Article
• Language: English
• Published: International Union of Crystallography 2020-03-01
• Series: IUCrJ
• Subjects: backfilling; mesoporous titania; semiconducting polymers; tellurophene; grazing incidence small-angle neutron scattering
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2052252520000913

Efficient infiltration of a mesoporous titania matrix with conducting organic polymers or small molecules is one key challenge to overcome for hybrid photovoltaic devices. A quantitative analysis of the backfilling efficiency with time-of-flight grazing incidence small-angle neutron scattering (ToF-GISANS) and scanning electron microscopy (SEM) measurements is presented. Differences in the morphology due to the backfilling of mesoporous titania thin films are compared for the macromolecule poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and the heavy-element containing small molecule 2-pinacolboronate-3-phenylphenanthro[9,10-b]tellurophene (PhenTe-BPinPh). Hence, a 1.7 times higher backfilling efficiency of almost 70% is achieved for the small molecule PhenTe-BPinPh compared with the polymer PTB7-Th despite sharing the same volumetric mass density. The precise characterization of structural changes due to backfilling reveals that the volumetric density of backfilled materials plays a minor role in obtaining good backfilling efficiencies and interfaces with large surface contact.