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

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-ethyl-hexyl)-thio-phen-2-yl)benzo[1,2-;4,5-']di-thio-phene-2,6-diyl--(4-(2-ethyl-hexyl)-3-fluoro-thieno[3,4-]thio-phene-)-2-carboxyl-ate-2-6-diyl)] (PTB7-Th) and the heavy-element containing small molecule 2-pinacol-boronate-3-phenyl-phen-anthro[9,10-]telluro-phene (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.