James W. E. Kneller

Accurate temperature measurements of a photovoltaic (PV) device are not always straightforward. Compromises between accuracy and spatial resolution often have to be made to give either quantitative single point measurements or qualitative spatial measurements. Phosphor thermometry is demonstrated in this work to measure the temperature of an encapsulated silicon photovoltaic device with uncertainty less than 1 °C. Comparisons with contact thermocouple probes are made under external white‐light illumination and internal resistive heating. Under similar conditions, phosphor thermal imaging shows less sensitivity to sources of uncertainty such as poor probe positioning and reduced thermal contact, allowing the detection of faults and shunt induced thermal hot spots in encapsulated PV devices with a higher degree of confidence.

The solid‐state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high‐performing diketopyrrolopyrrole‐based polymers. By synthesizing a series of DPP‐based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face‐on/edge‐on orientation, which allows the formation of 3D carrier channels in an otherwise edge‐on‐oriented polymer chain network. Time‐of‐flight measurements performed on the various polymer films support this hypothesis by showing higher out‐of‐plane carrier mobilities for the partially face‐on‐oriented polymers. Additionally, a favorable morphology is mimicked by blending a face‐on polymer into an exclusively edge‐on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices.