Plasmonic Enhancement of Biosolar Cells Employing Light Harvesting Complex II Incorporated with Core–Shell Metal@TiO₂ Nanoparticles

Abstract

photosynthetic complexes in artifi cial phototovoltaic (PV) devices as "green" light harvesting antennas was proposed in hopes to use their extraordinarily efficient light absorption and energy transfer properties. Measurable photocurrent was initially achieved using a self-assembled membrane of RCs, [ 2,3 ] LHCI-RC core complexes, [ 4 ] or whole photosystems (PSI or PSII) [ 3,5 ] on conductive electrodes. The power conversion effi ciency (PCE) was increased notably after incorporating the photosynthetic complexes into the PV cells. [ 6,7 ] Light-harvesting complex II (LHCII) extracted from green plants is the major antenna complex in photosystem II (PSII). As a subunit, LHCII has much simpler structure and smaller size than the composite photosystems. It accounts for about half of the chlorophylls (Chls) in the thylakoid. The natural form of LHCII is a trimer consisting of three monomers each of which comprises a polypeptide of about 232 amino-acid residues, some light-absorbing pigments (8 Chl a , 6 Chl b , and 3-4 carotenoids) and one phospholipid. [ 8 ] The protein structure precisely confi nes the pigments in proper positions to generate strong coupling with each other, which enables high effi ciency in harvesting and transfering solar energy. [ 9 ] A LHCII layer inserted at the heterojunction of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid (PCBM) in a solid-state PV cell has claimed to show ≈30% enhancement in the photocurrent and the internal quatum effi ciency. [ 10 ] Other studies have utilized LHCII trimers as photosensitizers to interface with semiconductive TiO 2 fi lm in fabricating economic and environment-friendly dye-sensitized solar cells (DSSCs). [ 7,11 ] The operation of such DSSCs mimics natural photosynthesis, with photons captured by the dye sensitizers in analogue to LHCs and charge separation occuring between sensitizer-TiO 2 interface in analogue to the RCs. Therefore DSSCs can be used as a model artifi cial device to exploit the energy conversion processes in photosynthetic proteins. Our previous work on assembling LHCII aggregates in a thin-fi lm DSSC has demostrated that the formation of charge transfer (CT) states in the aggregated LHCIIs can facilitate faster electron injection from LHCII to TiO 2 , leading to higher electron collection effi ciency of the PV system. [ 12 ] Here the study of effects of plasmonic nanoparticles (PNPs) conjugated with natural extract light-harvesting complex II (LHCII) is reported. Three types of core-shell metal@TiO 2 PNPs with distinct surface plasmonic resonance are prepared. The plasmonic adsorption of the metal core provides strong photon capture and enhances the LHCII excitation through plasmon-induced resonance energy transfer (PIRET). More effi cient charge separation is facilitated at LHCII/TiO 2 interface as revealed by quenching of the fl uorescence and reduction of the fl uorescence lifetime of LHCII after adsorbing on PNPs. Femtosecond transient absorption provides further conclusive proof for charge injection from exci...

TiO2: A Critical Interfacial Material for Incorporating Photosynthetic Protein Complexes and Plasmonic Nanoparticles into Biophotovoltaics

“…This hierarchical architecture was demonstrated to suppress electron recombination with tri-iodide along with increase of electron lifetime and perform no hindering in mass transport using ionic liquid electrolyte. Recently, we employed a similar anatase TiO 2 nanotree array as photoanode scaffold for the LHCII sensitized biophotovoltaic cells [25]. This TiO 2 nanotree array can be simply grown on TiO 2 coated FTO glass by one-pot hydrothermal reaction without necessity of high-tech equipment [26].…”

“…It was recently reported that strong LHCII attachment can be obtained on a APTES grafted FTO substrate via electrostatic interaction between the anionic residues on the stromal side with cationic ─NH 3 + groups [14]. We adopted this approach and used APTES to functionalize the surface of TiO 2 thin film, TiO 2 nanotree array photoanodes and TiO 2 -encapsulated plasmonic NPs in LHCII sensitized solar cells [25]. Clear improvement in protein attachment is indicated by the more intense and uniform greenish color on the APTES modified photoanode (Figure 8a).…”

“…Noble metal nanoparticles, that is, gold or silver nanoparticles, have been explored to enhance the solar cell performance utilizing their surface plasmonic resonance (SPR) effects that can enormously alter the optical absorption and emission of photosynthetic proteins near the nanoparticle surface [48]. An example of such solar cells is shown in Figure 11 [25]. Enhancement of light absorption was observed for PSI attached to plasmonic nanoparticles (PNPs) [49].…”

In-situ phase transition to form porous h-MoO3@C nanofibers with high stability for Li+/Na+ storage

“…Carbon composite structures have been widely studied, such as core shell structure [38][39][40], which is considered as an effective structure to solve the above problems. For instance, Xia et al [41] synthesized MoO 3 /C nano-composites with a capacity of about 500 mA h g −1 at the 100 th cycle at a current density of 0.1 A g −1 for LIBs.…”

Correlation of the plasmon-enhanced photoconductance and photovoltaic properties of core-shell Au@TiO2 network

“…11 We have also confirmed such effects in the DSSCs sensitized with natural light harvesting complex II. 12 In most DSSC operations, these three effects are mixed. It is necessary to design some model systems to elucidate the contributions of these distinctive effects in order to understand the complex mechanisms of the plasmon-enhanced DSSCs.…”