Efficient electrical doping of organic semiconductors is a necessary prerequisite for the fabrication of high performance organic electronic devices. In this work, we study p-type doping of poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) spin-cast from two different solvents. Using electron diffraction, we find strong dopant-induced π−π-stacking for films from the solvent chloroform, but not from chlorobenzene. This image is confirmed and expanded by the analysis of vibrational features of P3HT and polaron absorptions using optical spectroscopy. Here, a red-shifted polaron absorption is found in doped films from chloroform, caused by a higher conjugation length of the polymer backbone. These differences result in a higher conductivity of films from chloroform. We use optical spectroscopy on the corresponding blend solutions to shed light on the origin of this effect and propose a model to explain why solutions of doped P3HT reveal more aggregation of charged molecules in chlorobenzene, whereas more order is finally observed in dried films from chloroform. Our study emphasizes the importance of solvent parameters exceeding the bare solubility of pure dopant and host material for the preparation of highly conductive doped films.

Hybrid solar cells based on organometal halide perovskite absorbers have recently emerged as promising class for cost- and energy-efficient photovoltaics. So far, unraveling the morphology of the different materials within the nanostructured absorber layer has not been accomplished. Here, we present the first visualization of the mesoporous absorber layer in a perovskite solar cell from analytical transmission electron microscopy studies. Material contrast is achieved by electron spectroscopic imaging. We found that infiltration of the hole transport material into the scaffold is low and inhomogeneous. Furthermore, our data suggest that the device performance is strongly affected by the morphology of the TiO2 scaffold with a fine grained structure being disadvantageous.