Papers by Alexandre Mantovani Nardes
Proceedings of SPIE, Oct 5, 2015
We have theoretically and experimentally investigated the effects of Ag-grating electrode on the ... more We have theoretically and experimentally investigated the effects of Ag-grating electrode on the performance of polymer:fullerene based bulk heterojunction organic solar cells. First, an integrated numerical model has been developed, which is capable of describing both the optical and the electrical properties simultaneously. The Ag-grating patterned back electrode was then designed to enhance the absorption in sub-bandgap region of P3HT:PCBM binary devices. Laser interference lithography and metal lift-off technique were adopted to realize highly-uniform and large-area nanograting patterns. We measured almost 5 times enhancement of the external quantum efficiency at the surface plasmon resonance wavelength. However, the overall improvement in power conversion efficiency was not significant due to the low intrinsic absorption of active layer in this sub-bandgap region. We, then, investigated about the effect of surface plasmon on the ternary device of P3HT:Si-PCPDTBT:ICBA. It was demonstrated that the infrared absorption by the Si-PCPDTBT sensitizer can be substantially enhanced by matching the surface plasmon resonance to the sensitizer absorption band. Besides, we also observed an additional enhancement in the visible range which is due to the scattering effect of the gratings. An overall short-circuit current enhancement of up to 40% was predicted numerically. We have then fabricated the device by the lamination technique and observed a 30% increase in the short circuit current. Plasmon enhancement of sensitized organic solar cell presents a promising pathway to high-efficiency, broadband-absorbing polymer:fullerene bulk heterojunction organic solar cells.
Organic Electronics, Dec 1, 2016
We introduce a simple methodology to integrate prefabricated nanostructuredelectrodes in solution... more We introduce a simple methodology to integrate prefabricated nanostructuredelectrodes in solution-processed organic photovoltaic (OPV) devices. The tailored "photonic electrode" nanostructure is used for light management in the device and for hole collection. This approach opens up new possibilities for designing photonically active structures that can enhance the absorption of sub-band gap photons in the active layer. We discuss the design, fabrication and characterization of photonic electrodes, and the methodology for integrating them to OPV devices using a simple lamination technique. We demonstrate theoretically and experimentally that OPV devices using photonic electrodes show a factor of ca. 5 enhancement in external quantum efficiency (EQE) in the near infrared region. We use simulations to trace the observed efficiency to surface plasmon polariton modes in the nanostructure.
We demonstrate that a post-annealing step results in enhanced open-circuit voltage (Voc) and fill... more We demonstrate that a post-annealing step results in enhanced open-circuit voltage (Voc) and fill factor (FF) and lower reverse saturation current (Js) that consequently increases the power conversion efficiency (PCE) of organic bulk-heterojunction (BHJ) devices by about 40 % as a result of better contact formation, as typically assumed. Although true, we show that additional device properties are affected as well. We found that annealing induces vertical phase segregation and consequently the enrichment of donor and acceptor materials at the correct electrical contact. In addition, a de-doping process and a decrease in defect density also take place and are the major causes for device improvement after post-annealing the OPV devices. Implications for OPV basic research and manufacturing are discussed.
ChemPhysChem, May 30, 2014
On p. 1539 N. Kopidakis et al. present a comparative study of the photophysical performance of a ... more On p. 1539 N. Kopidakis et al. present a comparative study of the photophysical performance of a prototypical fullerene derivative with a planar small molecule acceptor in an organic photovoltaic device. The shapes of the molecules determine the performance of the device in more than one way.
Macromolecules, Feb 5, 2013
ABSTRACT A series of new donor–acceptor π-conjugated copolymers incorporating 5,10-dihydroindolo[... more ABSTRACT A series of new donor–acceptor π-conjugated copolymers incorporating 5,10-dihydroindolo[3,2-b]indole (DINI) as an electron donating unit have been designed, synthesized, and explored in bulk heterojunction solar cells with diketopyrrolopyrrole and thienopyrroledione as the electron accepting units. A significant effect of the size and shape of the pendant alkyl substituents attached to the DINI unit on the optical and electronic properties of the copolymers is described. Our study reveals a good correlation between the theoretical calculations performed on the selected materials and the experimental HOMO, LUMO, absorption spectra, and band gap energies of the corresponding copolymers. The band gaps of the conjugated copolymers can be tailored over 0.4 eV by the electron-withdrawing nature of the different acceptor units to provide better overlap with the solar spectrum, and the energy levels can be tuned 0.2 eV depending on the alkyl substituents employed. For the polymers in this study, a nonoptimized power conversion efficiency as high as 3% was observed.
Advanced Functional Materials, May 11, 2011
MRS Proceedings, 2001
ABSTRACTHydrogenated amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon films are indispen... more ABSTRACTHydrogenated amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon films are indispensable materials for large area electronic devices like solar cells, image sensors and thin film transistors (TFTs). The interest of the µc-Si:H films arise from the fact that they combine the high optical absorption of a-Si:H and the electrical transport properties close to those of crystalline silicon. In this work we show the correlation between substrate deposition temperature, crystallinity and electrical properties of a-Si:H and µc-Si:H films. The films were prepared by a conventional PECVD (13.56 MHz) RF system from PH3/SiH4/H2 gas mixtures in the temperature range of 100 to 250°C. While phosphorus doped (n) a-Si:H are deposited yielding conductivity values no better than 10−2 S/cm, (n) µc-Si:H layers deposited at substrate temperature of 250°C show conductivity values higher than 101 S/cm, crystalline fraction up to 80% and Hall mobility of about 0.9 cm2. V−1.s−1. It was observed ...
Advanced Functional Materials, Mar 25, 2008
for providing materials and discussions. A. M. Nardes acknowledges the Alban Program (the Europea... more for providing materials and discussions. A. M. Nardes acknowledges the Alban Program (the European Union Programme of High Level Scholarships for Latin America, ID#E03D19439BR) for the financial support.
Materials Science and Engineering: C, 2004
In this work, a plasma-enhanced chemical vapor deposition (PECVD) system was used to deposit carb... more In this work, a plasma-enhanced chemical vapor deposition (PECVD) system was used to deposit carbon nitride at low deposition temperatures (ca. 100 8C) to improve the lifetime of polymer light-emitting diodes (PLEDs) and to decrease photo-degradation of MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinilene]) in air. The characteristics of the carbon nitride and MEH-PPV films are investigated with FTIR and UV-Visible spectroscopies, with particular emphasis on the degradation process of MEH-PPV under illumination. It was shown by absorbance measurements that the coating protects the polymer film since the damage caused by photooxidation diminishes considerably. Current vs. voltage curves for PLEDs also indicated that the protection of a carbon nitride layer enhances the device lifetime.
ACS applied materials & interfaces, Jan 21, 2015
Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their ext... more Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their extended electronic wave functions, they often form semicrystalline thin films. In this work, we aim to understand whether distribution of crystallographic orientations affects exciton diffusion using a low-band-gap polymer backbone motif that is representative of the donor/acceptor copolymer class. Using the fact that the polymer side chain can tune the dominant crystallographic orientation in the thin film, we have measured the quenching of polymer photoluminescence, and thus the extent of exciton dissociation, as a function of crystal orientation with respect to a quenching substrate. We find that the crystallite orientation distribution has little effect on the average exciton diffusion length. We suggest several possibilities for the lack of correlation between crystallographic texture and exciton transport in semicrystalline conjugated polymer films.
Chemistry of Materials, 2015
ABSTRACT We report on the effect of humidity on the structural, optical, and electrical propertie... more ABSTRACT We report on the effect of humidity on the structural, optical, and electrical properties of formamidinium lead halide perovskite (FAPbI3; prepared by a solvent engineering method) and the device characteristics of planar FAPbI3 solar cells. The relative humidity strongly affects the perovskite film morphology, which changes from a uniform, fully covered FAPbI3 film at low relative humidity (e.g., ~2%) to an inhomogeneous film consisting of many voids (or pinholes) at high humidity (30%-40%). This morphological deterioration with increasing humidity is also accompanied by a reduction of the film crystallinity, decay of optical property, and shorter carrier lifetime. The device based on a planar FAPbI3 film shows the best conversion efficiency of 16.6% (with the stabilized output efficiency of 16.4%) at a low humidity (~2%). Higher humidity leads to lower device performance, mainly due to the loss of open-circuit voltage and fill factor, which is consistent with the decrease of recombination resistance.
Applied Physics Letters, 2014
ABSTRACT We report an 11.4%-efficient perovskite CH3NH3PbI3 solar cell using low-cost molybdenum ... more ABSTRACT We report an 11.4%-efficient perovskite CH3NH3PbI3 solar cell using low-cost molybdenum oxide/aluminum (i.e., MoOx/Al) as an alternative top contact to replace noble/precious metals (e.g., Au or Ag) for extracting photogenerated holes. The device performance of perovskite solar cells using a MoOx/Al top contact is comparable to that of cells using the standard Ag top contact. Analysis of impedance spectroscopy measurements suggests that using 10-nm-thick MoOx and Al does not affect charge-recombination properties of perovskite solar cells. Using a thicker (20-nm) MoOx layer leads to a lower cell performance caused mainly by a reduced fill factor. Our results suggest that MoOx/Al is promising as a low-cost and effective hole-extraction contact for perovskite solar cells.
2011 37th IEEE Photovoltaic Specialists Conference, 2011
Admittance spectroscopy is commonly used to characterize majority-carrier trapping defects. In to... more Admittance spectroscopy is commonly used to characterize majority-carrier trapping defects. In today's practical photovoltaic devices, however, a number of other physical mechanisms may contribute to the admittance measurement and interfere with the data interpretation. Such challenges arise due to the violation of basic assumptions of conventional admittance spectroscopy such as single-junction, ohmic contact, highly conductive absorbers, and measurement in reverse bias. We exploit such violations to devise admittance spectroscopy-based methods for studying the respective origins of "interference": majority-carrier mobility, non-ohmic contact potential barrier, minority-carrier inversion at heterointerface, and minority-carrier lifetime in a device environment. These methods are applied to a variety of photovoltaic technologies: CdTe, Cu(In,Ga)Se2, Si HIT cells, and organic photovoltaic materials.
Advanced Energy Materials, 2010
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Journal of Applied Physics, 2014
ABSTRACT The nanoscale light control for absorption enhancement of organic photovoltaic (OPV) dev... more ABSTRACT The nanoscale light control for absorption enhancement of organic photovoltaic (OPV) devices inevitably produces strongly non-uniform optical fields. These non-uniformities due to the localized optical modes are a primary route toward absorption enhancement in OPV devices. Therefore, a rigorous modeling tool taking into account the spatial distribution of optical field and carrier generation is necessary. Presented here is a comprehensive numerical model to describe the coupled optical and electrical behavior of plasmon-enhanced polymer: fullerene bulk heterojunction (BHJ) solar cells. In this model, a position-dependent electron-hole pair generation rate that could become highly non-uniform due to photonic nanostructures is directly calculated from the optical simulations. By considering the absorption and plasmonic properties of nanophotonic gratings included in two different popular device architectures, and applying the Poisson, current continuity, and drift/diffusion equations, the model predicts quantum efficiency, short-circuit current density, and desired carrier mobility ratios for bulk heterojunction devices incorporating nanostructures for light management. In particular, the model predicts a significant degradation of device performance when the carrier species with lower mobility are generated far from the collecting electrode. Consequently, an inverted device architecture is preferred for materials with low hole mobility. This is especially true for devices that include plasmonic nanostructures. Additionally, due to the incorporation of a plasmonic nanostructure, we use simulations to theoretically predict absorption band broadening of a BHJ into energies below the band gap, resulting in a 4.8% increase in generated photocurrent. (C) 2014 AIP Publishing LLC.
2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014
We present a comprehensive numerical model to describe the coupled optical and electrical behavio... more We present a comprehensive numerical model to describe the coupled optical and electrical behavior of plasmon-enhanced polymer/fullerene bulk heterojunction solar cells. We incorporate a bound electron/hole pair generation rate that is dependent on both the 2-dimensional position within the P3HT:PCBM active layer, and the solar spectral irradiance. By considering the absorption and plasmonic properties of two different popular device architectures, and applying the Poisson, current continuity, and drift/diffusion equations, we are able to predict quantum efficiency, short-circuit current density, and desired carrier mobility ratios for devices possessing strongly non-uniform optical fields commonly produced by nanostructures.
2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014
We have theoretically demonstrated an enhanced infrared absorption of the sensitizer in ternary p... more We have theoretically demonstrated an enhanced infrared absorption of the sensitizer in ternary polymer solar cell by introducing silver gratings at the back metal electrode. A combined model which incorporates the complex optical absorption profile and the electrical transport of the generated charge carriers was successfully developed. Using this model, we considered Si-PCPDTBT as an infrared sensitizer for P3HT:ICBA bulk heterojunction solar cells. A silver grating feature was optimized to produce a highly localized optical field inside the active polymer layer and enhance the infrared absorption of the sensitizer. Finally, an overall short-circuit current enhancement of about 40% is obtained theoretically.
Advanced Energy Materials, 2011
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Papers by Alexandre Mantovani Nardes