In situ interface engineering for probing the limit of quantum dot photovoltaic devices.

Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells

Effect of the electrophoretic deposition of Au NPs in the performance CdS QDs sensitized solar cells

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability alternative for next generation of solar cells, and metallic nanoparticles had shown to be a good alternative to improve specific parameters in such kind of devices. In the present work, it is showed the systematic study of the effect of electrophoretic gold nanospheres (Au NPs) with cadmium sulfide Quantum Dots (CdS QDs) sensitized TiO2 solar cells. Au NPs were added by electrophoretic deposition at several times (0.5, 2.5 and 7.5 minutes) and CdS QDs were deposited by a Successive Ionic Layer Absorption and Reaction (SILAR) method. Electrophoretic deposition allowed to significantly decrease the Au NPs deposition times respect previously reported methods. The results show that Au NPs reduce the photocurrent (from 9.85 to 9.44 mA/cm2) at the same time that increase the open circuit voltage (Voc) (from 575 to 618 mV) and the Fill Factor (FF) (from 46 to 51%) which result in a final increase of the photoconversion efficiency (η) (from 2.63 to 2.96% for 0.5 min of deposit). A systematic characterization permitted to identify the origin of the variations observed in the solar cell parameters with and without Au NPs. Incident Photon to Current conversion efficiency (IPCE) demonstrate that the Au NPs reduces the amount of light that reach the CdS QDs and Impedance Spectroscopy (IS) analysis, indicates a downshift in the TiO2 conduction band (CB) and decreases the recombination processes, resulting in the observed increase in the FF and Voc.We acknowledge financial support from CONACYT through grant 134111, the UC-MEXUS program grant 00007, the European Community Seven Framework Program (FP7- 428 NMP-2010-EU-MEXICO), CIO-UGTO 2013–2015 and the CEMIE-Solar (04002) consortium. D. Esparza, and A. Ceja acknowledge scholarship from CONACYT and thanks to Maria Christian Albor for SEM and EDS analysis. Isaac Zarazúa thanks to CONACYT for the postdoctoral fellow

Amphiphilic Anionic Pt(II) Complexes: from spectroscopic to morphological changes

A new class of amphiphilic anionic platinum(II) bzimpy complexes has been demonstrated to show aggregation in water through PtfflfflfflPt and π–π stacking interactions. An interesting aggregation–partial deaggregation–aggregation process and a morphological transformation from vesicles to nanofibers have been demonstrated. These changes can be systematically controlled by the variation of solvent composition and could readily be probed by UV-vis absorption, emission, NMR, transmission electron microscopy and even with our naked eyes ...postprin

Quantum dot-sensitized solar cells

Quantum dot-sensitized solar cells (QDSCs) have emerged as a promising candidate for next-generation solar cells due to the distinct optoelectronic features of quantum dot (QD) light-harvesting materials, such as high light, thermal, and moisture stability, facilely tunable absorption range, high absorption coefficient, multiple exciton generation possibility, and solution processability as well as their facile fabrication and low-cost availability. In recent years, we have witnessed a dramatic boost in the power conversion efficiency (PCE) of QDSCs from 5% to nearly 13%, which is comparable to other kinds of emerging solar cells. Both the exploration of new QD light-harvesting materials and interface engineering have contributed to this fantastically fast improvement. The outstanding development trend of QDSCs indicates their great potential as a promising candidate for next-generation photovoltaic cells. In this review article, we present a comprehensive overview of the development of QDSCs, including: (1) the fundamental principles, (2) a history of the brief evolution of QDSCs, (3) the key materials in QDSCs, (4) recombination control, and (5) stability issues. Finally, some directions that can further promote the development of QDSCs in the future are proposed to help readers grasp the challenges and opportunities for obtaining high-efficiency QDSCs

Nanowire Photoelectrochemistry.

Recent applications of photoelectrochemistry at the semiconductor/liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run

量子ドット太陽電池とペロブスカイト太陽電池における界面修飾と界面電荷ダイナミクス

The present globalization of energy shortage and environmental pollution issues have posed a grave menace to human survival and development. Finding a viable supply of clean, renewable energy is one of the most daunting challenges facing the world. Solar cells as devices that convert solar energy into electricity is the focus of the whole society. However, conventional solar cells have had limited impact in meeting this challenge because of their high pollution, high cost and low power conversion efficiencies. Recently, colloid quantum dot solar cells (CQDSCs) and perovskite solar cells (PSCs) as new generation solar cells have been attracting immense attention owing to their inexpensive solution-based techniques and high theoretical power conversion efficiency. However, stability is still a big problem for CQDSCs and PSCs, and charge dynamics in those solar cells are not clear. To obtain stable CQDSCs and PSCs through interface modification, and reveal the charge dynamics in those solar cells are the central aim of this thesis. This thesis investigated the surface ligand dependent charge carrier dissociation, charge carrier transmission and recombination of CQDSCs, and used novel hole transport materials to modify the interface of CQDSCs and PSCs to reduce the interfacial recombination in CQDSCs and PSCs. In this thesis, I explore a method to obtain air stable PbSe CQDs and surface ligand dependent exciton dissociation, recombination, photovoltaic property, and stability of PbSe solid films and CQDSCs. I select four short ligands, that is, two organic ligands 1,2-ethanedithiol (EDT) and 3-mercaptopropionic acid (MPA); two inorganic ligand cetyltrimethylammonium bromide (CTAB) and tetrabutylammonium iodide (TBAI) to investigate the ligand-dependent air stability, energy level shift, the exciton dissociation, and photovoltaic properties of PbSe CQDSCs. In addition, the charge transfer rate, recombination processes and carrier lifetimes in these CQDSCs were also revealed through ultrafast transient absorption (TA) spectra, and open-circuit transient voltage (Voc) decay measurements. We also explore a method to suppress the interfacial recombination at QDs/Au electrode in CQDSCs by using organic small molecule. We develop a novel donor-π-donor (D-π-D) organic small molecule bis-triphenylamine with spiro(fluorene-9,9’-xanthene) as the conjugated system, named BTPA-4, as a hole selective layer (HSL) in the PbS CQDSCs. We found that the introduction of BTPA-4 as HSL can enhance the open-circuit voltage (Voc), prolong the effective carrier lifetime, reduce the interfacial recombination at PbS QDs/Au interface, and hence improve the device performance. Furthermore, the PbS CQDSCs with BTPA-4 possessed a noticeably stable property for over 100 days of storage under ambient atmosphere that has been the Achilles\u27 heel of other organic HSL for CQDSCs. We also focus on hole transport materials and the interfacial recombination in PSCs. Three triphenylamine-based hole-transport materials (HTMs), named BTPA-4, BTPA-5 and BTPA-6, were used into PSCs. BTPA-6 with four substituted triphenylamine units exhibited a better solar cell performance than BTPA-4 and BTPA-5 which contain two substituted triphenylamine units. BTPA-6 achieved a PCE of 14.4% which nearly matches Spiro-OMeTAD (15.0%). The order of the recombination resistance was found to be in the order of BTPA-4 < BTPA-5 < BTPA-6 < Spiro-OMeTAD, indicating that the electron blocking capability of the HTM is in this order. This trend agrees with the Voc trend of their corresponding solar cells. In addition, BTPA-6 based devices showed better long-term stability than that with Spiro-OMeTAD, which can partially be attributed to the hydrophobicity of BTPA-6 is better than that of Spiro-OMeTAD. The goal of above experiments is to gain a more complete understanding of charge carrier dynamics in CQDSCs and PSCs, so that more efficient materials and architecture for solar cells can be designed in the future.電気通信大学201

NIR-emissive Alkynylplatinum(II) Terpyridyl Complex as a turn-on selective probe for heparin quantification by induced helical self-assembly behaviour

The extent of self-assembly viametal–metal and π-π stacking interactions, induced by the polyanionic biopolymers, enables the class of alkynylplatinum(II) terpyridyl complexes to be applicable for the sensing of important biomacromolecules through the monitoring of spectral changes. Strong demand arises for the design of selective and practical detection techniques for the quantification of heparin, a highly negative-charged polysaccharidethat can function as anticoagulant, due to the prevention of hemorrhagic complications upon overdose usage.Aconvenient sensing protocol for the detection of UFH and LMWH, two common forms of heparins in clinical use, in buffer and biological medium has been demonstrated with the spectral changes associated with the induced self-assembly of a NIR-emissive platinum(II) complex. The detection range has been demonstrated to cover clinical dosage levels and the structurally similar analogues can be effectively differentiated based on their anionic charge density and the formation of supramolecular helical assembly of the platinum(II) complex with them ...postprin