A novel architecture with high‐aspect‐ratio nanoscale metallic periodic patterns is fabricated as transparent electrodes. The structure shows high visible light transmission and has superior electrical conductivity compared to standard indium tin oxide (ITO) coated glass. A proof‐of‐principle organic photovoltaic device is successfully fabricated with the electrode.

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To understand the effect of processing conditions such as spin coating speed and drying rate on the density of defects; poly͑3-hexylthiophene͒:fullerene-derivative solar cells A, B, and C were fabricated with solvent drying times of ϳ40 min, 7 min, and 1 min, respectively. We show that slowest grown device A has one order of magnitude less subband gap traps than device C. The open circuit voltage and its light intensity dependence was strongly affected by interfacial recombination of carriers at subgap defect states. The losses due to trap-assisted recombination can even dominate over bimolecular recombination, depending on the density of defect states

In the global search for clean, renewable energy sources, organic photovoltaics (OPVs) have recently been given much attention. Popular modern-day organic solar cells are made from solution-processable, carbon-based polymers (e.g. the model poly(3-hexylthiophene) that are intimately blended with fullerene derivatives (e.g. [6,6]-phenyl-C 71-butyric acid methyl ester) to form what is known as the dispersed bulk-heterojunction (BHJ). This BHJ architecture has produced some of the most effi cient OPVs to date, with reports closing in on 10% power conversion effi ciency. To push effi ciencies further into double digits, many groups have identifi ed the BHJ nanomorphology-that is, the phase separations and grain sizes within the polymer: fullerene composite-as a key aspect in need of control and improvement. As a result, many methods, including thermal annealing, slow-drying (solvent) annealing, vapor annealing, and solvent additives, have been developed and studied to promote BHJ self-organization. In this review, the authors present an overview of these methods and summarize the results they have enabled.

Interest in realizing conjugated polymer-based films with controlled morphology for efficient electronic devices, including photovoltaics, requires a parallel effort to characterize these films. Scanning angle (SA) Raman spectroscopy is applied to measure poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM)-blend morphology on sapphire, gold, and indium tin oxide interfaces, including functional organic photovoltaic devices. Nonresonant SA Raman spectra are collected in seconds with signal-to-noise ratios that exceed 80, which is possible due to the reproducible SA signal enhancement. Raman spectra are collected as the incident angle of the 785 nm excitation laser is precisely varied upon a prism/sample interface from approximately 35 to 70°. The width of the ∼1447 cm(-1) thiophene C═C stretch is sensitive to P3HT order, and polymer order varied depending on the underlying substrate. This demonstrates the importance of performing the spectroscopic measurements on substrates and configurations used in the functioning devices, which is not a common practice. The experimental measurements are modeled with calculations of the interfacial mean square electric field to determine the distance dependence of the SA Raman signal. SA Raman spectroscopy is a versatile method applicable whenever the chemical composition, structure, and thickness of interfacial polymer layers need to be simultaneously measured.

Herein, the implications of silicone contamination found in solution-processed conjugated polymer solar cells are explored. Similar to a previous work based on molecular cells, we find this contamination as a result of the use of plastic syringes during fabrication. However, in contrast to the molecular case, we find that glass-syringe fabricated devices give superior performance than plastic-syringe fabricated devices in poly(3-hexylthiophene)-based cells. We find that the unintentional silicone addition alters the solution's wettability, which translates to a thinner, less absorbent film on spinning. With many groups studying the effects of small-volume additives, this work should be closely considered as many of these additives may also directly alter the solutions' wettability, or the amount of silicone dissolved off the plastic syringes, or both. Thereby, film thickness, which generally is not reported in detail, can vary significantly from device to device. KEYWORDS: organic, photovoltaic, solar, polymer, silicone, plastic, PDMS, P3HT ■ INTRODUCTIONIn the global search for clean and sustainable energy sources, organic photovoltaics (OPVs) have recently gained much attention. Facets such as solution processability, light weight, low cost, and the potential for roll-to-roll production make OPVs an advantageous option for the realization of greenpower generation. Popular modern-day organic solar cells are fabricated in what is known as the dispersed bulk-heterojunction (BHJ) architecture, formed from blends of conjugated polymers or small molecules with fullerene derivatives. 1 Since its introduction in the mid-1990s, many groups have suggested numerous methods for increasing BHJ power conversion efficiency (PCE). Among these are small-volume additives, in which a macromolecule or solvent are mixed with the BHJ blend at percentages typically less than 10%. 2−10 Most of these reports cite an improved morphology as the reason behind performance improvement, whether it is increased mobility from larger grain sizes, or increased exciton dissociation from smaller grain sizes. What is generally overlooked is how an additive changes the wetting of the BHJ blend solution on the substrate surface. As we show in this work, additive-induced differential wetting can lead to a notable change in film thickness, which alone can significantly affect light absorption and photocurrent generation. Moreover, films of different thicknesses dry at different rates, which in turn can affect the internal BHJ morphology and other device parameters. Thus, an additive-induced differential wetting can significantly affect device performance, without playing a direct role in altering morphology of the bulk BHJ film. We showcase the above using silicone as a small-volume additive, which is unintentionally introduced by plastic-syringes widely used in OPV fabrication.Recently, a work by Graham et al. showed that silicone contamination, induced during fabrication by the use of plastic syringes, can act as a small-volume additive. 2...

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Organic photovoltaics (OPVs) are primary candidates for economical and flexible next-generation solar electricity conversion devices. However, efficiencies of the OPVs are limited, among other reasons, by poor charge transport and limited acceptor materials. To overcome this, hybrid organic-inorganic solar cells have been proposed. In this study, the authors investigated the photovoltaic characteristics of hybrid amorphous silicon (a-Si:H) films with varying doping nature with poly(3-hexylthiophene) (P3HT) only and P3HT:phenyl-C61-butyric acid methyl ester (PCBM) bulkheterojunction-based solar cells. Both intrinsic and doped a-Si:H films were used. Despite the higher short circuit current density of P3HT/intrinsic a-Si:H device, the charge collection and open circuit voltage in P3HT/n+ a-Si:H device were the highest. This was attributed to favorable band bending and high built-in electric field in P3HT. Previously proposed model for photovoltaic mechanism in polymer/a-Si:H devices was revisited, and a revision was proposed. P3HT:PCBM cells on the three types of cells largely followed the same trend as the P3HT-only devices, except that intrinsic device did not have a photocurrent contribution from the organic layer. Nanomaterials and Energy Volume 2 Issue NME4 Effect of a-Si:H-polymer interface on the behavior of hybrid solar cells Mahadevapuram, Dalal and Chaudhary