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8th World Conference on Photovoltaic Energy Conversion; 313-315, The aim of this work is the study of the degradation of two different PSCs. A PSC with undoped SnO2 ETL was compared to a PSC with ETL made of G-SnO2. Degradation was monitored by performing both impedance spectroscopy and dark I-V measurements. Experimental data were collected just immediately after fabrication and after one week. It was observed that the degradation of the solar cells affects both the AC behavior of the devices, modifying associated Nyquist plots, and the DC behavior, observable from dark current-voltage curves. From the Nyquist plots a quantitative analysis was performed by comparing the parameters of a proper equivalent circuit model. Results were coherent with those achieved with DC analysis, thus providing that the arising from these two techniques allows to gain a deeper knowledge of the degradation phenomena.

8th World Conference on Photovoltaic Energy Conversion; 409-411, The aim of this work is the study of beneficial effects of HNO3 doping for G/Si SJSCs by means of capacitance versus voltage (C-V) curves and impedance spectroscopy characterizations. Capacitance curves in forward bias allowed to characterize defects distribution at graphene/silicon interface, proving induced defect passivation of molecular doping. Impedance spectra both at reverse and forward bias enforced achieved results. Degradation after storing the solar cell in air was also monitored using the same techniques. AC analyses performed were confirmed by dark current-voltage (I-V) curves collected before doping, after doping and 2 weeks after doping storing cell in air.

In Schottky barrier solar cell (SBSC), the interface between absorber and front electrode plays a vital role for reducing the dark current, blocking the majority carriers injected into the electrode at forward bias, reducing surface recombination and passivating the silicon surface. In this respect, the addition of interfacial layer between the semiconductor absorber and the metal electrode can reflect into an improvement of the device performance. Here we combine n-type crystalline silicon with stacks of graphene and graphene-based derivative (GBD) layers with different properties, in order to realize efficient SBSCs. Graphene layers with different structure, work function and electrical conductivity, were obtained by varying the chemical vapor deposition (CVD) parameters: conductive graphene films were grown at 1070 °C, GBD interfacial layers at 790 °C. The stacked structures were fabricated by the multiple transfer of these films. The films and the stacks were characterized by Raman spectroscopy. The device with the GBD interlayer (acting as hole transport layer) exhibits promising performances in terms of external quantum efficiency (EQE) and power conversion efficiency (PCE, ~5 %). Doping treatments with nitric acid vapor was performed and improved the cell PCE up to 6.7 %. © 2018 AMSE Press. All rights reserved.

In this work, we report on a reliable fabrication strategy, based on the dip coating technique, for integrating a microgel monolayer onto the nanostructured optical fiber tip in a controlled fashion. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for controlling the probes responsivity to a pre-defined target parameter. Specifically, in the case study of Lab-on-Fiber plasmonic probes, we demonstrated that microgel coverage factors exceeding 90% allow to optimize the probe responsivity to both temperature and pH, chosen as benchmark stimuli. Moreover, with the aim of providing a design tool for MG assisted devices, we also propose an analytical model describing the light-MG layer interaction, as a function of the external stimulus applied. Overall, this study opens the way for the development of engineered microgels assisted Lab-on-Fiber probes for sensing applications. © OSA 2018 © 2018 The Author(s)

In this work a silicon based hybrid junction solar cell with a transparent conductive oxide (TCO) as top contact and including a layer composed by 3-aminopropyltriethoxysilan (APTES) and soluble graphene oxide (GO) with the structure of TCO/AGO/Si (where the layer formed by APTES and GO is referred to as AGO) was fabricated and tested. The realized structure had the typical scheme of a metal-insulatorsemiconductor silicon based solar cell where the conventional metal front contact was substituted with a ZnO:Al (AZO) transparent layer and a low-cost and easy-to-fabricate insulating layer (AGO) replaced the conventional interfacial SiOx layer. The analysis of the photovoltaic parameters allowed to put in evidence the beneficial effect of the fully transparent top contact as well as the role of the AGO interfacial layer. In particular, the measured external quantum efficiency of the AZO/AGO/Si solar cell reached values above 80% in the central part of the visible spectrum, with a short circuit current of about 30mA/cm2, while the power conversion efficiency resulted more than two times higher than that of the device without the incorporation of the AGO layer. The coupling, for the first time at our knowledge, of a TCO layer and a GO layer in a silicon based solar cell, opens the door for several applications in photovoltaic and other optoelectronic devices.

Schottky barrier solar cells based on graphene/n-silicon heterojunction have been fabricated and characterized and the effect of graphene molecular doping by HNO3 on the solar cells performances have been analyzed. Different doping conditions and thermal annealing processes have been tested to asses and optimize the stability of the devices. The PCE of the cells increases after the treatment by HNO3 and reaches 5% in devices treated at 200 °C immediately before the exposition to the oxidant. Up to now our devices retain about 80% of efficiency over a period of two weeks, which represents a good stability result for similar devices. © 2014 AEIT.

31st European Photovoltaic Solar Energy Conference and Exhibition; 700-703, The amorphous/crystalline silicon heterojunction solar cells have largely demonstrated to be high efficiency capable. Despite the highest efficiency cells are based on high quality n-type c-Si absorber, the p-type hold more than 90% of the world silicon solar cell market, so it seems important to improve device and cost efficiency using p-type substrates. An issue of is related to the amorphous layer absorbance so different materials have been studied and tested as replacing emitter to obtain a gain in terms of transmittance, conductivity and Jsc. We have adopted a different and wider bandgap emitter based on silicon oxide, n-SiOx. A central role in this type of structure is played from the chosen TCO workfunction, whose value affects strongly the heterojunction’s band structure at the emitter interface. RF magnetron sputtered TCO obtained with different deposition parameters, have been made in order to optimize their use in our heterojunction solar cell. Numerical simulation on the SiOx HJ, with TCO having proper workfunction value, show potential efficiency conversion well over the 23%.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1588-1591, Polymer solar cells (PSCs) are typically fabricated with a transparent conductive anode covered by a thin hole conducting layer, such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), over which, the active layer and low-work-function metals (usually Ca/Al) are deposited. This configuration suffers from degradation in operative conditions due to the degradation of PEDOT:PSS and metal cathode. In order to avoid these issues, the inverted configuration (where the charge collection nature of the electrodes is reversed avoiding the use of not stable layers) can be used. In this work we realized standard and inverted PSCs based on poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b']dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl]/[6,6]-phenyl C71 butyric acid methyl ester (PBDTTT-C:[70]PCBM) blend films. In the standard architecture, the transparent indium tin oxide (ITO) electrode is coated with PEDOT:PSS and used as a hole collecting electrode, while in an inverted device configuration, the ITO electrode is turned into the electron collecting contact by surface modification with zinc oxide (ZnO). The standard cells sequence is ITO/PEDOT:PSS/PBDTTT-C:[70]PCBM/Ca/Al and the inverted cells one is ITO/ZnO/PBDTTT-C:[70]PCBM/MoO3/Ag. We studied the electrical behavior (by means of IV-light and external quantum efficiency measurements) of both kinds of devices in order to investigate the influence of the architecture (standard vs inverted) on the performance of the PSCs.

29th European Photovoltaic Solar Energy Conference and Exhibition; 924-927, The main goal of amorphous/crystalline silicon heterostructure technology is the very high open circuit voltage obtainable because of the band bending at the doped amorphous/crystalline silicon (a-Si:H/c-Si) interface and the use of a thin intrinsic amorphous silicon buffer layer between them. Several limitations still affect the a-Si:H/c-Si heterostructure based on p-type c-Si wafer, among which the surface defect state density mainly originated by unsaturated dangling bonds. In this work we analyze the passivation effect of different thin film silicon based materials, grown by means of PECVD, and its behavior after thermal treatments. Different growth regimes for a-Si:H films have been used by varying hydrogen dilution (SiH4/H2) and the effective minority carriers lifetime has been measured by means of quasi-steady-state photoconductance technique. Alternative a-SiOx:H based buffers have been also considered. Lifetimes above 1 ms have been reached. Intrinsic layer passivation effectiveness has been tested on silicon heterojunction devices.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2005-2008, In this paper wet anisotropic texturing and subsequent smoothing of c-Si wafers, 350 and 100 μm thick, are investigated for reducing light reflection and improving light confinement within silicon substrate suitable for amorphous/ crystalline silicon heterojunction solar cells. The influence of time of the etching process used in the smoothing procedure is studied. To this aim reflectance measurements and scanning electron microscopy images are used to evaluate the surface morphology after the chemical etching.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1877-1881, The way to reach the grid parity for PV passes through the high efficiency solar cell technology. The amorphous/crystalline heterojunction promises the goal, considering the world record efficiency targeted by Panasonic. Transparent conducting oxides (TCOs) play an essential role in modern optoelectronic devices through their combination of electrical conductivity and optical transparency. TCO, plays a key role to enhance the HJ cell efficiency. We have studied and characterized the properties of a new trilayer AZO/Ag/AZO as TCO in the c-Si heterojunction solar cell, whose thickness and composition combination ensure also an antireflection coating role. The influence of Ag layer thickness on electrical and optical properties of the tri-layer film was investigated. Several analytical tools such as fourpoint probe, scanning electron microscopy (SEM) and ultraviolet–visible–near infrared (UV–vis–NIR) spectrophotometer were used to explore the causes of the changes in optoelectronic properties and surface micrographs. The highest value is 2.5×10−4Ω cm for the AZO (100nm) /Ag (8nm) /AZO( 50nm) tri-layer film, and the sheet resistance is 15.5 Ω/sq, while the average transmittance is above 78% in the visible light region (400–800 nm).

28th European Photovoltaic Solar Energy Conference and Exhibition; 340-343, One of the most reputable applications of graphene is in the field of solar cells because of its notable performances as transparent electrode and active layer for electron-hole separation in photovoltaic devices. In the present paper we fabricate and characterize graphene/n-crystalline-silicon heterojunctions with simple planar thin-film geometry. The rectifying behaviour of the devices is verified through the acquisition of dark current-voltage curves. External quantum efficiencies (EQE) have also been measured to evaluate the charge separation and collection, as a result of the Schottky barrier formed at the interface between graphene and silicon. Our devices show EQE values over 50% for wavelengths in the range 400 nm<

27th European Photovoltaic Solar Energy Conference and Exhibition; 2907-2910, Polymer solar cells have evolved as a promising cost-effective alternative to silicon-based ones. However, low efficiency of these plastic devices limits their feasibility for commercial use. The efficiencies of polymer photovoltaic cells got a major boost with the introduction of the bulk heterojunction (BHJ) configuration consisting of an interpenetrating network of electron donor and acceptor materials. Recently, benzodithiophene based polymers has been used as electron donors in polymer solar cells showing very promising properties such as an increasing charge transport and a red shift of the absorption spectra. In this work the synthesis, the spectroscopic and photovoltaic characterization of a copolymer based on (octylsulfanyl)bithiophene and benzo[1,2-b:4,5-b’]dithiophene units and a polymer based on (butylsulfanyl)bithiophene unit are reported. BHJ solar cells using these polymers as donor materials blended with [70]PCBM as acceptor were prepared and investigated. The geometry of the device is: glass/ITO/PEDOT:PSS/blend/Ca/Al. The electrical performances of the cells were compared in order to study the influence of the benzodithiophene unit on the polymer backbone. The power conversion efficiency of the best realized polymer solar cell is 2.3% under 100 mW/cm2 AM 1.5G illumination.

26th European Photovoltaic Solar Energy Conference and Exhibition; 749-752, The aim of this work is to present a procedure for assessing the degradation of Concentration Photovoltaic (CPV) modules, equipped with silicon solar cells operating outdoors in real-time conditions, by measuring various PV module performance parameters before the cells are deployed outdoors and periodically afterwards. To understand the origin of these degradation modes and how they affect the performances of the concentration cells is an essential step to improve their reliability and to accelerate their competitiveness.