15722 Phys. Chem. Chem. Phys., 2012, 14, 15722–15728 This journal is c the Owner Societies 2012 Cite this: Phys. Chem. Chem. Phys., 2012, 14, 15722–15728 Cu nanoparticles enable plasmonic-improved silicon photovoltaic devicesw Michele L. de Souza, ab Paola Corio a and Alexandre G. Brolo* b Received 2nd October 2012, Accepted 5th October 2012 DOI: 10.1039/c2cp43475j This work examines the effect of copper nanoparticles (Cu NPs) on the photocurrent efficiency of silicon photovoltaic (Si PV) devices. An optimized synthesis of stable Cu NPs is reported together with a procedure for their immobilization on the Si PV surface. A comprehensive analysis of the photocurrent and power dependence of the Cu NPs surface coverage and size is presented. A decrease in photoconversion was observed for wavelengths shorter than B500 nm, due to the Cu interband absorption. In the low surface coverage limit, where the level of aggregation was found to be low, the surface plasmon resonance absorption dominates leading to a modest effect on the photocurrent response. As the number of aggregates increased with the surface coverage, the photocurrent efficiency also increased, and a maximum enhancement power conversion of 16% was found for a 54  6 NPs per mm 2 PV cell. This enhancement was attributed to SPR light scattering and trapping into the Si PV device. Higher surface coverage yielded numerous aggregates which acted as a bulk coating and caused a decrease in both photocurrent and power measurements. Introduction Photovoltaic (PV) devices are bound to play a major role in addressing our future energy needs. 1 However, the current generation of PVs still suffers from shortcomings that affect their viability as an economic alternative energy solution. 2 The main commercially relevant types of PVs are silicon (Si)-based, and they are classified as first and second generation cells. 2 The first generation cells are fabricated on approximately 300 mm thick monocrystalline or multicrystalline Si wafers. The second generation cells are constructed using 1 to 3 mm Si film deposited over a variety of materials, such as plastic, glass or metals. Second generation cells offer obvious advantages in terms of material costs. 2 Light losses in Si PVs, due to surface reflectivity, poor absorption or scattering processes, are considered one of the issues that need to be overcome. Improved light absorption and trapping in first generation Si PVs are achieved by surface texturing. 3 This procedure is available for thick solar cells that can afford B5–10 mm of Si removal in order to yield a structured surface. 3 Texturing promotes light trapping through internal scatterings which enhances the light endurance in the device. This strategy is not as convenient for second generation, thin film, Si PVs. In that case, texturing by generating surface irregularities results in increased electron–hole (e  –h + ) pair recombination, which is a loss mechanism that correlates with the increased surface area. 4 Anti-reflection (AR) coating is also implemented in PVs to improve light absorption. 5 Alternative strategies concerning the light trapping and absorption on both first and second generation Si PVs are an active area in solar cell research. Plasmonic integration with solar cells corresponds to one of the most promising ap- proaches to address the light absorption and trapping issues. 6 Plasmonic structures are metallic nanomaterials that support surface plasmon resonances (SPR), which are collective oscillations of the conducting electrons in those subwavelength structures. Incident light that matches the SPR energy is strongly scattered and absorbed, and the magnitude of the extinction (the term ‘‘extinction’’ means the combination of these two processes: scattering + absorption) depends on the geometric characteristics of the structure, such as size and shape of the metallic nanoparticles (NPs). 7 These are features that can be tuned by the appropriate fabrication procedure. The plasmonic properties are well-known to improve spectro- scopic properties for species adsorbed on metallic surfaces, such as in the surface-enhanced Raman scattering (SERS) effect. 7,8 The application of plasmonics to improve photocurrent response in PV devices is currently a very active research area. 9–11 Stuart and Hall pioneered this field by employing B100 A ˚ thick Au, Ag and Cu (metals that support SPR in the visible range) annealed islands, over a thin silicon-on-insulator (SOI) device. 9,12 The presence of the metallic nanoparticles a Instituto de Quı´mica, Universidade de Sa ˜o Paulo, Av. Prof. Lineu Prestes, 748, Cidade Universita ´ria, 05513-970, Sa ˜o Paulo, SP, Brazil. E-mail: michele.souza@usp.br, paola@iq.usp.br; Fax: +55 11 3091 3890; Tel: +55 11 3091 3853 b Department of Chemistry, University of Victoria, V8W 3V6, P.O. Box 3065, Victoria, BC, Canada. E-mail: agbrolo@uvic.ca; Fax: +1 250 721-7147; Tel: +1 250 721-7167 w Electronic supplementary information (ESI) available. See DOI: 10.1039/c2cp43475j PCCP Dynamic Article Links www.rsc.org/pccp PAPER Downloaded by University of Victoria on 07 November 2012 Published on 10 October 2012 on http://pubs.rsc.org | doi:10.1039/C2CP43475J View Online / Journal Homepage / Table of Contents for this issue