We report the use of direct (hetero)arylation polymerizations (DHAP) as a means of obtaining 3,4-propylenedioxythiophenebased conjugated polymers for use in electrochromics. This method offers a rapid route to achieving polymers in high yields with simplified purification procedures and low residual metal content, as determined by inductive coupled plasma-mass spectrometry (ICP-MS). The studied polymers possess comparable electrochromic properties to those previously reported by our group, implying that their switching ability from a colored to a transmissive state is independent of the residual metallic impurities.

The effect of air processing, with air exposure varying from minutes to hours prior to encapsulation, on photovoltaic device performance has been studied through a series of electrical characterizations and optical simulations for a donor/acceptor polymer-based organic solar cell based on poly(dithienogermole-alt-thienopyrrolodione) p(DTG-TPD)/PC71BM blends. A ∼10% degradation in power conversion efficiency was observed due to air processing with 10 min exposure time, with AM1.5 power conversion efficiencies (PCEs) decreasing from 8.5 ± 0.25% for devices processed in inert nitrogen atmosphere to 7.7 ± 0.18% for devices processed in ambient air. After 3 h air exposure, the PCE leveled off at 7.04 ± 0.1%. This decrease is attributed partially to interface issues caused by exposure of the electrode materials to oxygen and water and partially to a degradation of the hole transport in the active layer.

An investigation of the recombination kinetics and the density of states distribution in bulk heterojunction organic photovoltaic cells was undertaken using impedance spectroscopy measurements under varying levels of illuminations. Three organic polymer solar cells were investigated which differed only by the p-type polymer used in the active layers while the device architecture and acceptor molecule (PC70BM) were kept the same. We found that the density of states profiles for the three cells are similar and can be superimposed by a horizontal shift due to a difference between the polymers' HOMO and the PC70BM's LUMO levels. The recombination mechanisms for the three cells showed the same behavior, suggesting an important role of the acceptor in this process; however, large differences in the absolute value of carrier lifetime τ eff related to the choice of the polymer are evident, indicating that the recombination kinetics depends on a combination of the properties of both materials and the morphology of their blend. ■ INTRODUCTIONEven though the power conversion efficiency of state of the art organic photovoltaics (OPVs) cells is still lower than their inorganic counterparts, there is a growing interest in transforming these cells from laboratory curiosities into commercial products. This interest is fueled by both (i) potential economically advantageous low production costs using fabrication techniques like roll-to-roll processing and inkjet printing and (ii) their potential use in new applications because of their light weight and flexibility. The power conversion efficiency values of single junction OPVs reported in the literature have been fast approaching the 10% mark, thanks to the many synthetic (i.e., new materials) and processing routes (i.e., morphology optimization, optimization of interfaces, etc.) available in the design of OPVs, which hold promise for further developments.The most successful device architecture used for OPV cells is based on the bulk heterojunction (BHJ).1,2 In BHJ cells, the active layer consists of a thin film (∼100 nm thick) of an interpenetrating network of an electron accepting material (generally a fullerene derivative) and an electron donating light absorbing material (generally a semiconducting polymer). BHJ cells are excitonic solar cells, where excitons (strongly bound hole−electron pairs) are generated by light absorption in the active layer. The strongly bound pairs cannot directly dissociate because of the low dielectric constant of the organic materials, and dissociation occurs only at the donor−acceptor interface due to the difference in electron affinities of the two materials (commonly taken to be larger than 0.3 eV). Since excitons are neutral species, they can move toward the interface only by diffusion, and to obtain an optimal energy conversion, the time necessary to diffuse to the interface has to be smaller than the exciton lifetime. Therefore an ideal morphology is that of a bicontinuous composite in which the interfacial area is maximized and th...

4,4'-Bis-(4-pentenyl)-dithieno[3,2-b:2',3'-d]germole was synthesized as a functional building block for the efficient preparation of dithienogermole (DTG) derivatives with varying alkyl chain lengths and pendant functionalities in excellent yields. These derivatives were efficiently isolated via olefin cross-metathesis followed by hydrogenation.