After more than a decade of organic photovoltaics making introductory steps into the market, the scientific and industrial communities keep working toward the consolidation of this technology in the market. The recent development of materials that yield simultaneously high levels of efficiency and transparency brings the opportunity to enter important niche markets, such as transparent photovoltaic windows, in which organic semiconductors might become the best alternative absorber. In this perspective, we provide an overview of the technological progress in organic photovoltaics especially relevant for target semitransparent applications, highlighting key R&D aspects that demand more attention from an industrial and product-development perspective. We conclude that strong effort is needed to develop higher-performing photoactive materials and roll-to-roll compatible interlayer materials and electrodes. Although this is already a significant research focus of the academic community, we identify that reinforcing research effort on topics such as improvement in device lifetime, color portfolio, and module design and efficiency will help in making a significant effect on changing the status of organic photovoltaics from a novel technology to a mature industry.

Small molecule organic semiconductors have well-defined structures and can be used in place of polymers which often show batch-to-batch variation. Many different electron-rich donor and electrondeficient acceptor units have been used to design materials with reduced HOMO-LUMO gaps and improved mobilities. Here we introduce a novel acceptor unit, 1-dodecyl-6-dodecoxynaphthyridine-2one. This acceptor unit has been used in the synthesis of two novel compounds, with thiophene and 2,1,3-benzothiadiazole (BT) cores. The BT-containing compound shows a narrower HOMO-LUMO gap, broad solid-state absorption and has been applied to organic field-effect transistors, showing a mobility of 0.022 cm V 1 s 1 after optimisation of devices using self-assembled monolayers. © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Small molecule organic semiconductors have well-defined structures and can be used in place of polymers which often show batch-to-batch variation. Many different electron-rich donor and electron-deficient acceptor units have been used to design materials with reduced HOMO-LUMO gaps and improved mobilities. Here we introduce a novel acceptor unit, 1-dodecyl-6-dodecoxynaphthyridine-2-one. This acceptor unit has been used in the synthesis of two novel compounds, with thiophene and 2,1,3-benzothiadiazole (BT) cores. The BT-containing compound shows a narrower HOMO-LUMO gap, broad solid-state absorption and has been applied to organic field-effect transistors, showing a mobility of 0.022 cm(2) V-1 s(-1) after optimisation of devices using self-assembled monolayers. (C) 2017 The Authors. Published by Elsevier B.V.

Degradation in polymer based organic solar cells still remains poorly understood despite prominent research efforts in recent years. In this work, the impact of photostability and documented morphological evolution of a couple of poly(benzodithiophene-diketopyrrolopyrrole) polymers in their blends with phenyl-C61-butyric acid methyl ester (PCBM) are investigated by a combination of charge extraction techniques. Photo-induced charge carrier extraction by linearly increasing voltage (photo-CELIV) and integral-time of flight (TOF) methods are employed to determine charge carrier mobility and recombination at various stages of photo-degradation in the absence of air. We report the progressive formation of deeper trap states as crucial outcome of photo-degradation within these blends as deduced from our measurements.

The impact of polymer side-chains on encapsulated OPV device stability is studied systematically in a series of low bandgap polymers.

The technology behind a large area array of flexible solar cells with a unique design and semitransparent blue appearance is presented. These modules are implemented in a solar tree installation at the German pavilion in the EXPO2015 in Milan/IT. The modules show power conversion efficiencies of 4.5% and are produced exclusively using standard printing techniques for large-scale production.

We have investigated the effects of thin-film morphology on the photovolatic performance for a series of donor–acceptor copolymers based on benzodithiophene donor and benzothiadiazole acceptor units. Photovoltaic devices incorporating polymer:fullerene blends show highest efficiencies (up to 6%) for those polymers exhibiting the least degree of crystallinity in X-ray diffraction patterns and a corresponding lowest surface roughness in thin films. We find that the existence of such crystalline domains in thin polymer films correlates well with spectral signatures of polymer chain aggregates already present in solution prior to casting of the film. Polymer solubility and casting conditions therefore appear to be crucial factors for enhancing efficiencies of photovoltaic devices based on such donor–acceptor copolymers. To examine why the presence of crystallite domains lowers device efficiencies, we measured exciton diffusion lengths by modeling the time-dependent photoluminescence from thin polymer films de...