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Organic photovoltaic (OPV) devices are promising tools for indoor light harvesting and power conversion, but high voltage losses, especially under weak illumination, hinder their development. In this work, the organic active material system PM6/IT-4Cl, which is green solvent processible and highly suitable for indoor light harvesting, is employed to investigate the voltage loss mechanism in indoor OPV devices. Three major problems specific to indoor OPV devices are identified, including a high density of pinholes in the active layer leading to low device shunt resistance, a too-large charge transfer energy loss causing high radiative voltage losses, and a high trap concentration in the active layer limiting the device electroluminescence efficiency and open-circuit voltage. To solve these problems, a strategy based on the use of solvents and solid additives is proposed. This resulted in a significant increase in power conversion efficiency (PCE) for the PM6/IT-4Cl devices from 16% to 23% under white LED illumination (3000 K, 4000 lux). Our findings highlight the importance of developing tailored optimization strategies to reduce voltage losses in order to further improve the performance of indoor OPV devices. [ABSTRACT FROM AUTHOR]

To increase the lifetime of organic photovoltaic (OPV) devices and pass European lifetime standards, some encapsulation systems are often used to limit the exposition to oxygen and humidity of solar cells. Despite this progress, the damages induced by the encapsulation process are scarcely studied in literature. In this article, the consequences of the common roll‐to‐roll and vacuum lamination approaches are investigated and compared. The losses of performances are first followed induced by both the encapsulation itself and in a damp heat ageing. The vacuum lamination seems harmless for the solar cells. However, a significant damage is evidenced, even with a relatively mild roll‐to‐roll encapsulation. The degradation mechanisms are further investigated by complementary imaging characterization tools: photoluminescence/electroluminescence imaging and spectroscopy, laser‐beam‐induced current mapping, and correlated to J(V) curves. The recent advancements in the optoelectronic domain may allow linking cell performance to localized flaws. It appears that, although the processing conditions are rather homogeneous, the resulting degradation ends up with a strong localization feature. [ABSTRACT FROM AUTHOR]

In this study, the optical, electrochemical, electrolumiscent, and photovoltaic properties of a series of poly( p-phenylene vinylene) (PPV) derivatives bearing different dendritic pendants, poly{2-[3′,5′-bis(2″-ethylhexyloxy)benzyloxy]-1,4-phenylenevinylene} (BE-PPV), poly{2-[2′,5′-bis(3″,7″-dimethyl)octyloxy]-1,4-phenylenevinylene} (BD-PPV), poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[3′,5′-bis(2″-ethylhexyloxy)benzyloxy]-1,4-phenylenevinylene}-co-poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (BE-co-MEH-PPV), and poly{2-[2′,5′-bis(3″,7″-dimethyl)octyloxy]-1,4-phenylenevinylene}-co-poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (BD-co-MDMO-PPV), were investigated. The steric pendants strongly affect the absorption spectra, photoluminescence (PL) sepctra, the onset oxidation/reduction potentials, and further affect the electrolumiscent and photovoltaic properties. Copolymerization can reduce the steric effect and improve the electrolumiscent and photovoltaic properties. The brightness of light-emitting diodes base on copolymer BE-co-MEH-PPV and BD-co-MDMO-PPV reached 3988 and 3864 cd/m2, respectively, much higher than that based on homopolymer BE-PPV (523 cd/m2) and BD-PPV (333 cd/m2), also higher than that based on MEH-PPV (3788 cd/m2). The power conversion efficiency (PCE) of solar cells based on BE-co-MEH-PPV and BD-co-MDMO-PPV reached 1.41, 0.76%, respectively, much higher than that based on BE-PPV (0.24%) and BD-PPV (0.14%). Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]