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.

Increasing the lifetime of polymer based organic solar cells is still a major challenge. Here, the photostability of bulk heterojunction solar cells based on the polymer poly[4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt -[2,5-bis(3-tetradecylthiophen-2-yl)thiazole[5,4-d]thiazole)-1,8-diyl] (PDTSTzTz) and the fullerene [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 60 BM) under inert atmosphere is investigated. Correlation of electrical measurements on complete devices and UV-vis absorption measurements as well as highperformance liquid chromatography (HPLC) analysis on the active materials reveals that photodimerization of PC 60 BM is responsible for the observed degradation. Simulation of the electrical device parameters shows that this dimerization results in a signifi cant reduction of the charge carrier mobility. Both the dimerization and the associated device performance loss turn out to be reversible upon annealing. BisPC 60 BM, the bis-substituted analog of PC 60 BM, is shown to be resistant towards light exposure, which in turn enables the manufacture of photostable PDTSTzTz:bisPC 60 BM solar cells.

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The photo-oxidation behavior of three different polymersnamely, poly(3-hexylthiophene) (P3HT), poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (C-PCPDTBT), and poly[2,6-(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-alt-4,7-(2,1,3-benzothiadiazole)] (Si-PCPDTBT)is investigated in neat polymer films and in blends with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for different polymer:PCBM ratios. PCBM is shown to have both stabilizing and destabilizing effects, the extent of which is dependent on the type of polymer with which it is blended. Screening of the polymer from incident light by PCBM turns out to play an only minor role in the stabilization of P3HT. Quenching of the polymer excited states is also not a significant stabilization mechanism, as demonstrated by the comparison of the reduction of photo-oxidation rates to the extent of photoluminescence quenching by PCBM and 2,7-dinitrofluorenone (DNF). Photoinduced absorption spectroscopy reveals that the enhanced degradation of C-PCPDTBT in blend films with PCBM correlates with the population of the polymer triplet state via the polymer:PCBM charge-transfer state.

A study of how light‐induced degradation influences the fundamental photophysical processes in the active layer of poly(3‐hexylthiophene)/[6,6]‐phenyl C61‐butyric acid methyl ester (P3HT/PCBM) solar cells is presented. Non‐encapsulated samples are systematically aged by exposure to AM 1.5 illumination in the presence of dry air for different periods of time. The extent of degradation is quantified by the relative loss in the absorption maximum of the P3HT, which is varied in the range 0% to 20%. For degraded samples an increasing loss in the number of excitons within the P3HT domains is observed with longer ageing periods. This loss occurs rapidly, within the first 15 ps after photoexcitation. A more pronounced decrease in the population of polarons than excitons is observed, which also occurs on a timescale of a few picoseconds. These observations, complemented by a quantitative analysis of the polaron and exciton population dynamics, unravel two primary loss mechanisms for the performances of aged P3HT/PCBM solar cells. One is an initial ultrafast decrease in the polaron generation, apparently not related to the exciton diffusion to the polymer/fullerene interface; the second, less significant, is a loss in the exciton population within the photoexcited P3HT domains. The steady‐state photoinduced absorption spectra of degraded samples exhibits the appearance of a signal ascribed to triplet excitons, which is absent for non‐degraded samples. This latter observation is interpreted considering the formation of degraded sites where intersystem crossing and triplet exciton formation is more effective. The photovoltaic characteristics of same blends are also studied and discussed by comparing the decrease in the overall power conversion efficiency of solar cells.

Due to their light weight, transparency and flexibility, organic photovoltaic (OPV) devices are ideal for building integration. As this application requires solar cell life times of more than twenty years and oxygen ingress cannot be avoided at competitive cost on this time scale, OPV modules must be intrinsically stabilized against photo-oxidation. To this end, the mechanism of rapid performance loss of OSCs due to oxygen-induced degradation must be understood. Here, we combine transient absorption experiments with electrical studies in P3HT:PCBM and Si-PCPDTBT:PCBM thin films and solar cells after controlled photo-oxidation, studying charge carrier dynamics on the femtosecond to millisecond time scale. We find that oxygen-induced degradation does not significantly influence charge generation, while its influence on charge recombination is strong in both materials. A dramatic retardation of charge recombination already at low levels of oxygen-induced degradation is attributed to a substantial reduction of charge mobilities. We also observe a significant increase of the background concentration of charge carriers with the level of degradation, which leads to a crossover from second order towards pseudo-first order recombination behaviour. Extraction is shown to be retarded even more strongly than recombination, possibly by a reduction of the extraction field by the background carriers. Overall, the recombination yield is increased with degradation, explaining the strong performance loss already at low degradation levels.

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Energy is a vital commodity for modern society, and it is clear that the growing demand must be satisfied using renewable sources. Traditional photovoltaics, relying exclusively on feed‐in tariffs, are inadequate as cost and logistics involved in transporting electricity from solar farms to locations where it is finally needed are undervalued. A more synergistic approach is required where alternative technologies start conforming to already existing objects or structures to generate power directly at the point of use. Organic photovoltaics's (OPV) unique characteristics make it a vital component in every product that demands energy. With that said, it is not of relevance to generate maximum energy, it is rather important to provide an adequate amount to power a desired application. However, it is finally important that functionality can be warranted over the lifetime of the product. This article provides a perspective on the durability of OPV from a product and integration standpoint with key insights into the driving factors for the commercialization of OPV. It is highlighted that stability is a complex topic involving many different aspects and that it cannot be broken down to just a simple efficiency decrease over time in consequence of device exposure to defined stress conditions.