In the race to higher OPV efficiencies it is crucial to understand and minimize performance losses

by Dirk Buchhauser

When speaking about improvements in Organic Photovoltaics, a perfect match between the donor and acceptor is a must to ensure a well-balanced charge generation and collection. Intrinsic chemical and morphological properties of organic active materials need to be precisely controlled, relying heavily on deep experimental analysis and modeling. With the recent introduction of so called NFAs (aka Non-Fullerene-Acceptors) as a replacement for conventional fullerene-based materials, the photocurrent generation was greatly enhanced leading to outstanding efficiencies approaching 20%. To push power conversion efficiencies even further, it is necessary to maximize the open-circuit voltage (Voc) as well. Such optimization of Voc requires understanding of associated loss mechanisms and how to minimize these losses.

One of the emerging experimental methods to successfully determine the causes of voltage loss in OPVs is the Fourier-Transformed-Photocurrent-Spectroscopy (FTPS). FTPS is used to probe tail states and charge transfer states in OPV devices that affect donor-acceptor energy level alignment responsible for the device’s open circuit voltage. Typically, these states are poorly populated and are difficult to experimentally detect requiring highly sensitive instrumentation. FTPS offers unprecedented resolution of these ultra-low signal intensities states.  

One of the most reliable and widely used FTPS systems that produces high impact results is the PECT-600 supplied by the Taiwanese company Enlitech. Enlitech is a professional manufacturer of scientific and metrological instruments since 2012. The PECT-600 is one of the most sensitive photocurrent spectroscopy systems on the market. It is able to probe ultra-low intensity absorption signals and processing them with customized software, to provide quantitatively analyzed results. Additionally, the system is easy to assemble and use, so scientists can immediately start probing their samples after a fast and efficient installation. A comprehensive training on fundamental principles and analytical skills is provided along with the tool. This is unique service on the market that ranges from helping with practical analysis skills and sharing spectroscopy manuscript writing experiences according to Enlitech. Today more than 50 scientific articles have been published using the PECT-600 system, while more than 2000 papers made use of Enlitech characterization devices in general.

An outstanding example of how the PECT-600 can help achieve outstanding results can be found in Nature Communications volume 10, 2515 (2019). In this contribution Dr. JH Hou’s group from ICCAS used the PECT-600 to study the increase in open-circuit voltage when adding chlorinated NFA. The introduced system revealed a higher Voc and increased photocurrent due to the significant reduction in non-radiative decay loss resulting in PCE = 16% OPV, which is an outstanding result.

OrganicPV.info is delighted to welcome Enlitech to the platform and would like to encourage all partners and followers to get in touch with Enlitech and learn about their advanced measurement systems as well as their broad knowledge. Based on this cooperation, Enlitech also welcomes all OrganicPV.info followers to discuss their specific needs in OPV research and development with them and to see how to further improve OPV technology together!

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