Stability Assessment on a 3% Bilayer PbS/ZnO Quantum Dot Heterojunction Solar Cell (original) (raw)
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The Journal of Physical Chemistry C, 2016
We fabricated the long term air stable PbSe colloidal quantum dots (CQDs) based planar heterojunction solar cells (FTO/TiO 2 /PbSe/Au) with relatively larger active area (0.25 cm) using tetrabutylammonium iodide (TBAI, I-) as ligand in solid state ligand-exchange process. For the first time, we have achieved the whole preparation process of the device in the ambient atmosphere from PbSe CQDs collection to PbSe colloidal quantum dot solar cells (CQDSCs) fabrication, then storage and in their following measurements. Especially, TBAI-treated PbSe CQDSCs exhibited a power conversion efficiency (PCE) of 3.53% under AM 1.5 G in air, and also a remarkable long term stability (more than 90 days) of their storage in ambient atmosphere has been identified. By contrast, 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA) and cetyltrimethylammonium bromide (CTAB, Br-) treated PbSe CQDSCs were further studied. The ligand-dependent exciton dissociation, recombination, energy level shift and air stability of PbSe CQDs treated with these different ligands were systematically investigated. It was noted that TBAI-treated PbSe CQDSCs exhibited suppressed recombination, faster charge transfer rate, and longer carrier lifetimes, which resulted in a higher power conversation efficiency (PCE) and long term air stability.
Highly Monodispersed PbS Quantum Dots for Outstanding Cascaded-Junction Solar Cells
High-performance cascaded-junction quantum dot solar cells (CJQDSCs) are fabricated from as-prepared highly monodispersed lead sulfide QDs. The cells have a high power conversion of 9.05% and a short-circuit current density of 32.51 mA cm −2. A reliable and effective stratagem for fabricating high-quality lead sulfide quantum dots (QD) is explored through a " monomer " concentration-controlled experiment. Robust QDSC performances with different band gaps are demonstrated from the as-proposed synthesis and processing stratagems. Various potential CJQDSCs can be envisioned from the band edge evolution of the QDs as a function of size and ligands reported here. Q uantum dots (QDs) are well-known as infinitesimal semiconducting nanocrystals with a physical size in the range of their Bohr radius. 1 Because of their discrete density of state, the band gap (ε gap) of QDs can be compatibly modified by manipulating their dimensions, which leads to extensive studies for optoelectronics applications. 2 In particular, facile solution processability and ε gap customizability to the solar spectrum makes QDs one of the most promising materials for future emerging solar cells. 3 Prevalent studies in QD solar cells (QDSCs), mainly concern lead sulfide (PbS) materials because of their large Bohr radius (20 nm) and wide band gap (ε gap) tuning range (0.4−1.5 eV). 4 Profiting from improved process technologies, i.e. better passivation and optimized p−n junction structure, remarkable power conversion efficiencies (PCEs) of ca. 10% have been achieved recently. 5,6 However, in spite of the demonstrated abilities and fascinating features in the QDSCs, there are still challenges which need to be addressed in terms of material quality control and device architecture design. 3 For instance, a vast number of works have been performed to synthesize high-quality PbS QDs, 7,8 but it is still a challenge to reproduce identical QDs from different batches, which hampers stable device performance. As one of the most promising QD device architectures, solar cells made from cascading various sizes of QDs have been proposed and tentatively studied. 9−13 However, because of poor size control of the QDs, to date, none of the works report good PCE performance. In this work, we elucidate an effective and reliable PbS QD synthesis protocol for fabricating high-performance and robust QDSCs. Through the systematic adjustment of the precursor concentration, in a fixed reaction temperature and quench time, a wide range of different sizes of colloidal PbS QDs is produced with a narrow size distribution and high reproducibility. The effects of quantum confinement and surface functionalization for different ligands and QD size is subject to a rationalization analysis. Finally, based on the understanding gained of the optical−electrical properties of as-prepared PbS QDs, three distinct sizes of PbS QDs are selected and fabricated into cascaded-junction solar cells (CJSC) under ambient air conditions. The device structure is illustrated in Figure 1a, which employs layers of different sizes of QDs treated with different ligands for tuning their relative band alignment and also photon energy absorption. The elaborately designed devices show impressively high PCE and short-circuit current density compared with those of previously reported devices. 5,6 The assembling of CJSC requires highly monodispersed PbS QDs with a range of different possible sizes, ensuring small coplanar charge transport barriers and distinct size-dependent optical properties. 2 QDs utilized in the light absorber layers
Performance of PbSe quantum dot based heterojunction solar cells: Dependence on ligand type
The Japan Society of Applied Physics, 2016
Univ. Electro-Commun., Kyushu Inst. Tech., Nanjing Tech. Univ., CREST JST Yaohong Zhang, Chao Ding, Shuzi Hayase,Yuhei Ogomi, Jin Chang, Taro Toyoda, Qing Shen, Email: shen@pc.uec.ac.jp Introduction Quantum dots (QDs) based solar cells have attracted more and more interests as a promising candidate for the next generation solar cells. Compared with conventional solar cells, QDs solar cells (QDSCs) are easier to prepare with low fabrication cost. Additionally, QDs present high extinction coefficients, tunable absorption spectra, and multiple exciton generation (MEG) effect. PbSe QDs have attracted attention due to their small bulk bandgap, high dielectric constant, and large exciton Bohr radius. However, the performance of PbSe based QDSCs tend to quickly degrade after the solar cells expose to air. Here, we found a modified method to synthesis air stable PbSe QDs and investigate the effect of ligand on the performance of PbSe QDSCs. Experimental Method Colloidal PbSe QDs were synthe...
Ligands affect the crystal structure and photovoltaic performance of thin films of PbSe quantum dots
Journal of Materials Chemistry, 2011
We have prepared thin films of PbSe quantum dots (QDs) featuring three different ligands, oleic acid (OA), butylamine (BA), and 1,2-ethanedithiol (EDT), which have pronounced affects on the arrangement and photovoltaic performance of the PbSe QDs in the thin films. Transmission electron microscopy revealed that ligands that altered the inter-QD spacing induced significant changes in the packing of the PbSe QDs in localized regions of small areas (300 Â 300 nm) of the thin films: from a superlattice of OA-capped PbSe QDs to a chaotic pattern of EDT-capped PbSe QDs. Using a synchrotron X-ray reflectivity probe and data fitting, we determined that the roughness decreased and the average densities increased for large-area (1.5 Â 1.5 cm) PbSe QD thin films capped with BA and EDT, relative to those of the OA-capped PbSe QD film. In particular, the PbSe QDs' vertical packing density, which is critical for charge transport, increased substantially for the system incorporating EDT ligands. As a result, devices containing the EDT-treated PbSe QD film as the active layer displayed much improved power conversion efficiencies (PCEs) relative to those of corresponding devices featuring either the OA-or BA-capped PbSe QD films as active layers. Adopting a layer-by-layer technique, we fabricated a EDT-capped PbSe QD device that exhibited a PCE of 2.45%.
Electrochimica Acta, 2016
Lead sulfide (PbS) quantum dot (QD) photovoltaics have reached impressive efficiencies of 12%, making them particularly promising for future applications. Like many other types of emerging photovoltaic devices, their environmental instability remains the Achilles heel of this technology. In this work, we demonstrate that the degradation processes in PbS QDs which are exposed to oxygenated environments are tightly related to the choice of ligands, rather than their intrinsic properties. In particular, we demonstrate that while 1,2-ethanedithiol (EDT) ligands result in significant oxidation of PbS, lead iodide/lead bromide (PbX 2) coated PbS QDs show no signs of oxidation or degradation. Consequently, since the former is ubiquitously used as a hole extraction layer in QD solar cells, it is predominantly responsible for the device performance evolution. The oxidation of EDT-PbS QDs results in a significantly reduced effective QD size, which triggers two competing processes: improved energetic alignment that enhances electron blocking, but reduced charge transport through the layer. At early times, the former process dominates, resulting in the commonly reported, but so far not fully explained initial increase in performance, while the latter governs the onset of degradation and deterioration of the photovoltaic performance. Our work highlights that the stability of PbS quantum dot solar cells can be significantly enhanced by an appropriate choice of ligands for all device components.
PbS QUANTUM DOT-BASED HETROJUNCTION SOLAR CELLS
2014
This study investigates the influence of nanoparticles (NPs) size on their optical properties, and the effect of combination of lead sulfide (PbS) quantum dots (QDs), with n-type and p-type NPs, on the photogenerated charge carriers transport across the heterojunction solar cell structure. PbS QDs, of a range of sizes, were synthesized using a co-precipitation process. In this study, p-type NPs, which are poly [3,4-ethylenedioxythiophene] –poly [styrenesulfonate] (PEDOT: PSS), copper oxide (CuO) and graphene oxide (GO); and n-type NPs which are zinc oxide (ZnO), titanium dioxide (TiO2), cadmium sulfide (CdS) and bismuth sulfide (Bi2S3), were synthesized and characterized by SEM and UV-visible spectrophotometers. The NPs with enhanced optical properties were utilized in heterojunction solar cell structures via spin coating, chemical bath deposition and SILAR cycle methods. The morphology and the theoretical band energy diagram for each cell were examined. The photovoltaic performance...
Comparing Halide Ligands in PbS Colloidal Quantum Dots for Field-Effect Transistors and Solar Cells
2018
Capping colloidal quantum dots (CQDs) with atomic ligands is a powerful approach to tune their properties and improve the charge carrier transport in CQD solids. Efficient passivation of the CQD surface, which can be achieved with halide ligands, is crucial for application in optoelectronic devices. Heavier halides, i.e., I– and Br–, have been thoroughly studied as capping ligands in the last years, but passivation with fluoride ions has not received sufficient consideration. In this work, effective coating of PbS CQDs with fluoride ligands is demonstrated and compared to the results obtained with other halides. The electron mobility in field-effect transistors of PbS CQDs treated with different halides shows an increase with the size of the atomic ligand (from 3.9 × 10–4 cm2/(V s) for fluoride-treated to 2.1 × 10–2 cm2/(V s) for iodide-treated), whereas the hole mobility remains unchanged in the range between 1 × 10–5 cm2/(V s) and 10–4cm2/(V s). This leads to a relatively more pro...
ZnO Nanowire Arrays for Enhanced Photocurrent in PbS Quantum Dot Solar Cells (Adv. Mater. 20/2013)
Advanced Materials, 2013
Solar cells employing colloidal quantum dots (QDs) have in recent years emerged as a promising third-generation photovoltaic technology. Quantum dot photovoltaic (QDPV) devices share many of the advantages of organic photovoltaics (OPVs), including low-temperature solution processing, environmentally abundant active materials, and compatibility with inexpensive and fl exible substrates. Although they remain less effi cient than OPVs, solid-state QDPVs have advanced faster, with AM1.5G power conversion effi ciencies climbing from 1.8% in 2008 to over 7% in 2012. A recent theoretical analysis of nanostructured thin-fi lm photovoltaics has suggested that single-junction QDPV effi ciencies of up to 15% may be practically achievable. Lead chalcogenide nanocrystals in particular could enhance the performance and practicality of QDPV devices, enabling bandgap tunability from the near infrared through the visible and, with lead sulfi de (PbS) QDs, stability in ambient atmosphere. Most recent high-performing QDPVs have paired PbS QDs with a wide-bandgap metal oxide window layer (i.e., ZnO or TiO 2 ) in an inverted np-heterojunction architecture (see a,b), [ 5 , 11 ] although Schottky junction devices with comparable performance have also been demonstrated using PbS and PbSe [ 12 , 13 ] QDs.