Charge transport layers in organic photovoltaics (OPV): challenges and opportunities for the large-scale deployment of OPV

Organic photovoltaics present a great opportunity to decarbonize the worlds energy generation. Due to their versatility in terms of colors, mechanical flexibility, light weight, containing abundant elements and the inherent flexibility of organic chemistry, on which they are based, they could allow for fast deployment of photovoltaics in hitherto not seen scenarios and at massive scales in potentially very short times. They have by now reached efficiencies of 14% on the scale of small modules though they are unfortunately still lacking behind other PV technologies, though a-Si modules, which still have niche applications like semi-transparent glassing actually has lower efficiencies. Beyond efficiency long lifetimes have been presented even for the latest high performing materials extrapolated under illumination of up to 30 years. By now there is also a broad understanding of the fundamental processes in organic solar cells. This applies to how charges are generated, as well as how they degrade. Though the broad strokes are well understood, there are many fine details still to be etched out, which will be important to further develop OPV in a more focused manner. As at present much of their development is still primarily driven by serendipitous exploration of new materials and processing methods. Especially in terms of the active layer materials. But beyond active layer materials also charge transport layers have gained a lot of focus in the resent years, as they can greatly impact stability and performance as well. In this work the agrivoltaics is presented as an interesting niche for upscaling of OPV and it is discussed in how far charge transport layers in such OPV devices are playing an important role in terms of their transparency, their impact on performance and stability. Finally a newly developed method is introduced for they analysis of JV-curves of solar cells for the fast detection of defects

Agrivoltaics—The Perfect Fit for the Future of Organic Photovoltaics

Abstract This Essay presents a possible pathway for the advancement of organic photovoltaics toward broader commercial success and enlarged market size. This vision aims at broad scale applications in photovoltaic greenhouses and polytunnels, which harvest those portions of the solar spectrum that are not used or required by plants. Based on the assumptions of the Shockley–Queisser–Limit, respectively detailed balance, and the additional postulation of using no absorption in the visible part of the AM 1.5G solar spectrum a power conversion efficiency of ≈17% is theoretically predicted. The suggestion is supported by the existence of a number of organic compounds, which already exhibit a good spectral compatibility with the typical photosynthetic action spectrum of chloroplasts. It is hoped that more suitable materials development shall be triggered and fertilized as a result of this Essay.A promising path is suggested for upscaling of organic photovoltaics (OPV) toward true mass application in the form of semi‐transparent OPV embedded in polytunnels or green‐houses. Here their specific properties, that is, offering narrow band absorption in the infrared wavelength range can be used as game changer. imag

Response to Christopher P. Muzzillo's Comments on “Introduction of a Novel Figure of Merit for the Assessment of Transparent Conductive Electrodes in Photovoltaics: Exact and Approximate Form”

Similarities and differences between figure of merits (FOMs) for the assessment of transparent conductive electrodes (TCEs) are discussed. This article is a response to C. P. Muzzillo's comment on the introduction of the novel FOM (the so‐called exact FOM or Anand's FOM) and it deals with questions about how implicit and how exact the different approaches really are and whether specific application cases can be covered or not. While the exact FOM has been introduced to provide an upper limit of photovoltaic power conversion efficiency for the whole range of possible transmittance and sheet resistance values of transparent conductive oxides, Muzzillo's comment points out specific application cases, that have to be treated with more individual modeling. In this work, the authors adopt these application cases into the exact FOM to demonstrate its applicability. Furthermore, the FOM approximation given by Muzzillo is used and slightly refined, yielding an even better agreement with the exact FOM. In the end, it is concluded that both approaches are justified: Muzzillo's FOM for very practical applications and Anand's (exact) FOM for fundamental assessment. In this work, both approaches have been harmonized to yield an ultimate tool for the future development of TCEs for photovoltaics

Performance and stability of organic solar cells bearing nitrogen containing electron extraction layers

Charge extraction and transport layers represent an important component of organic solar cells. Many different material groups are reported for these layers. Two important classes are metal oxides and organic materials. Many of these organic materials which are used as electron extraction layers (EELs) are nitrogen containing. Therefore, it has been decided to study a broad array of—to the largest part so far not reported—amine and imine containing organic materials as EELs in organic solar cells and compare them with an archetypical metal oxide electron transport layer (ETL). It enables certain structure–property relationships to be obtained for the EELs and to understand what determines their performance to a large part. Furthermore, their effect on the stability of organic solar cells is studied and they are found to be reasonable replacements as a cheap, quickly processable, environmentally friendly, biocompatible, and biodegradable alternative as compared with ETLs

Improved hole extraction selectivity of polymer solar cells by combining PEDOT:PSS with WO 3

As the device performance and stability of polymer solar cells strongly depend on the interfacial charge extraction layers, the hole transport layer (HTL) properties are crucial. Furthermore, unfavorable interactions with the electrode or the photoactive layer should be screened and prevented. Organic solar cells of conventional architecture by varying the HTL material and layer stack systematically between PEDOT:PSS and a sol–gel‐derived tungsten oxide (WO 3 ) are investigated. The impact of various HTLs in the solar cells is investigated by optical and electrical characterization. Interestingly, a triple‐layer WO 3 /PEDOT:PSS/WO 3 configuration results in the best device performance specifically compared with the use of pristine WO 3 and pristine PEDOT:PSS hole extraction layers. The triple layer also shows an increased reproducibility in the lifetime, which, combined with the improvement in the efficiency, can be the keys for expectable revenue

Compatible Solution‐Processed Interface Materials for Improved Efficiency of Polymer Solar Cells

Abstract The electron transport layer (ETL) in an organic solar cell is one of the main components that play a crucial role in the extraction of charges, improving efficiency, and increasing the lifetime of the solar cells. Herein, solution‐processed PBDTTT‐C‐T:PC71BM‐based organic solar cells are fabricated using conjugated PDINO molecules, sol‐gel derived under stoichiometric titanium oxide (TiOx), and a mixture of the same as an ETL. For PBDTTT‐C‐T:PC71BM‐based organic solar cells, a blend of organic‐inorganic ETLs demonstrates reduced bimolecular recombination and trap‐assisted recombination than a single ETL of either two materials. Furthermore, in both, fullerene and nonfullerene systems, the efficiency of the devices employing the blend ETL as compared to the single ETLs show some performance improvement. The strategy of integrating compatible organic and inorganic interface materials to improve device efficiency and lifetime simultaneously, and demonstrate the universality of different systems, has potential significance for the commercial development of organic solar cells

Performance and Stability of Organic Solar Cells Bearing Nitrogen Containing Electron Extraction Layers

Charge extraction and transport layers represent an important component of organic solar cells. Many different material groups are reported for these layers. Two important classes are metal oxides and organic materials. Many of these organic materials which are used as electron extraction layers (EELs) are nitrogen containing. Therefore, it has been decided to study a broad array of—to the largest part so far not reported—amine and imine containing organic materials as EELs in organic solar cells and compare them with an archetypical metal oxide electron transport layer (ETL). It enables certain structure–property relationships to be obtained for the EELs and to understand what determines their performance to a large part. Furthermore, their effect on the stability of organic solar cells is studied and they are found to be reasonable replacements as a cheap, quickly processable, environmentally friendly, biocompatible, and biodegradable alternative as compared with ETLs