PL Images Research Articles

Effect of back opening ratio and layout design on the performance of laser ablated point contact cell

In this paper we investigate the effect of the opening ratio and the back layout design on the electrical performance of the solar cell. First, the point contact solar cells are optimized by adjusting the laser opening ratio and the virtual-to-real ratio on each grid line of back side. The experimental results show that the open-circuit voltage (Voc) of the solar cell increases as the opening ratio decreases. Analysis of the PL images also shows that the damage to the passivation layer causes the Voc to drop. By characterizing the resistance of the back line, we found that laser drilling can cause an increase in the resistance of the back line. This can also lead to the FF loss. Then, by reducing the contact area of the bus-bar at the backside, the carrier recombination of the solar cell is reduced and the Voc of the cell is increased, resulting in a 0.07% increase in cell efficiency. Finally, the simulation shows that the openings lead to an increase in the recombination current (J01) at the base of the cell, which affects the efficiency of the cell.

Comparison of Outdoor and Indoor PL and EL Images in Si Solar Cells and Panels for Defect Detection and Classification

Comparison of Outdoor and Indoor PL and EL Images in Si Solar Cells and Panels for Defect Detection and Classification

Effect of Sub-Surface Damage Layer Removal by Sublimation Etching of 4H-SiC Bulk Wafers on PL Imaging of Crystal Defect Visibility

Improving the visibility of defects in nitrogen-doped 4H-SiC (0001) bare wafers by photoluminescence imaging (PLI) is essential for improving the epitaxial growth process and device yields. This study proposes sub-surface damage (SSD) introduced during the mechanical process of SiC wafers as a new factor in reducing defect visibility in PL images. To verify the effect of SSD, we observed the surface of a SiC wafer, which was thermally etched at about 3 μm. As a result, dramatic defect visibility improvement was observed when the surface roughness was sufficiently flat (Ra < 0.3 nm) after thermal etching. Thus, the results suggest that defect visibility in PL images can be improved by controlling SSD and surface roughness. Using the background noise reduction effect of the SSD removal, not only PLI but also many other wafer surface inspections are expected to be improved.

Trion confinement in monolayer MoSe2 by carbon nanotube local gating

We have successfully confined trions into a one-dimensional restricted space of a MoSe2 device with carbon nanotube (CNT) gate electrodes. The dry transfer process, including deterministic dry transfer of aligned CNTs, has led to an hBN-encapsulated MoSe2 device with CNT back gate electrodes. In contrast to a location without CNT gate electrodes, applying voltage via CNT gate electrodes significantly alters PL spectra at a location with CNT gate electrodes. PL imaging has revealed that image contrast from trions is linear along the CNT electrode underneath, consistent with 1D confinement of trions in response to the CNT local gating. The confinement width obtained from the PL image is 5.5 × 102 nm, consistent with nanoscale 1D confined trions with the diffraction limit broadening. This work has demonstrated electrical control of excitonic states at the nanoscale, leading to novel optoelectronic properties and exciton devices in the future.

Accelerated reliability tests of n+ and p+ poly-Si passivated contacts

We report on the stability of encapsulated, low-pressure chemical vapor-deposited phosphorus ( n + poly-Si) doped and boron ( p + poly-Si) doped poly-Si/SiO x passivated contacts by exposing the samples to three different accelerated tests: damp heat test, thermal cycling and ultraviolet exposure, adhering closely to the IEC 61215 standard. Outdoor testing was also performed by exposing the samples in the outdoor testing field at the National Renewable Energy Laboratory, and preliminary data accumulated for 1000 h from February to April of 2021 is reported. We studied non-metallized, thermally-metallized, and screen-printed n + and p + poly-Si by monitoring the effective minority carrier lifetime at the implied maximum power point using a Sinton lifetime tester, and recorded photoluminescence images before and after the exposure. The samples were found to be stable under all test conditions, which is encouraging for incorporation of these contacts in next-generation industrial silicon solar cells. • Three accelerated tests performed on encapsulated LPCVD n + and p + poly-Si/SiO x , adhering closely to IEC 61215 standard. • Samples include non-metallized, thermally metallized, and screen-printed n + and p + poly-Si/SiO x . • Effective minority carrier lifetime and PL images of the sample monitored. • All samples found to be stable after the exposure to accelerated and outdoor tests.

Growth of low-cost and high-quality monocrystalline silicon ingots by using split recycled seeds

In this work, we proposed a new method of seed recycling for casting monocrystalline silicon ingots. Different regions at the bottom of the monocrystalline silicon bricks were cut for controlling its size and crystal defects, which were used as recycled seeds and reasonable splicing to induce grain boundaries. The results showed that the recycled seeds with higher concentration of metal impurities will result in a longer red zone and the yield of mono-Si ingot would be slightly decreased. The defect density in the recycled seeds increased significantly, but decreased greatly during the seeding and growth. The defect distribution in PL images at the top of ingots grown with recycled seeds was similar to that of ingots grown with new seeds. Furthermore, the average cell efficiency of the solar cells fabricated by the wafers grown with recycled seeds was only 0.1% different from that of the wafers grown with new seeds. Therefore, this low-cost seed recycling method is of great significance for reducing the cost of cast monocrystalline silicon.

An Optically Reconfigurable Förster Resonance Energy Transfer Process for Broadband Switchable Organic Single-Mode Microlasers

An Optically Reconfigurable Förster Resonance Energy Transfer Process for Broadband Switchable Organic Single-Mode Microlasers

Deterministic positioning of nanophotonic waveguides around single self-assembled quantum dots

The capability to embed self-assembled quantum dots (QDs) at predefined positions in nanophotonic structures is key to the development of complex quantum photonic architectures. Here, we demonstrate that QDs can be deterministically positioned in nanophotonic waveguides by pre-locating QDs relative to a global reference frame using micro-photoluminescence ($\mu$PL) spectroscopy. After nanofabrication, $\mu$PL images reveal misalignments between the central axis of the waveguide and the embedded QD of only $(9\pm46$) nm and $(1\pm33$) nm, for QDs embedded in undoped and doped membranes, respectively. A priori knowledge of the QD positions allows us to study the spectral changes introduced by nanofabrication. We record average spectral shifts ranging from 0.1 to 1.1 nm, indicating that the fabrication-induced shifts can generally be compensated by electrical or thermal tuning of the QDs. Finally, we quantify the effects of the nanofabrication on the polarizability, the permanent dipole moment and the emission frequency at vanishing electric field of different QD charge states, finding that these changes are constant down to QD-surface separations of only 70 nm. Consequently, our approach deterministically integrates QDs into nanophotonic waveguides whose light-fields contain nanoscale structure and whose group index varies at the nanometer level.

(Invited) Synthesis and Properties of Giant Molecular Carbon Nanorings and Nanocrowns Based on Nanographenes

Carbon exists as a variety of nanometer-sized allotropes, such as 0D fullerenes, 1D carbon nanotubes (CNTs), and 2D graphene. So far, it is still a great challenge to construct CNTs with a fixed length and diameter-specified single-chirality. We have synthesized a series of novel large π-extended molecular carbon nanorings and nanocrowns based on nanographene hexa-peri-hexabenzocoronene (HBC) unit (named as [n]CHBCs) and other nanographenes as a finite model of armchair CNTs, including [n]CHBCs (n=4,6,8), TCR, and HCR, et al (Figure 1).1-3 Their tubular structures of these [n]CHBCs have also been characterized using various physical methods, including NMR, STM, PL, crystallographic analysis, and STM images. In addition, the photophysical properties of these nanocarbons are studied in solution and explained by theoretical calculations. TCR and HCR can selectively capture fullerene C60 due to strong supramolecular interactions and the molecular structure of C60@TCR is unambiguously determined by single-crystal X-ray diffraction. Compared to the HBC monomer, obvious redshift in absorption and emission spectra has been observed in these HBC carbon nanorings and nanocrowns. More recently, we constructed a three-dimensional capsule-like HBC-containing carbon nanocage,4 which can be considered as a novel synthetic model of the capped zigzag [12,0] carbon nanotubes. 1. Lu, D. P.; Wu, H. T.; Dai, Y. F.; Shi, H.; Shao, X.; Yang, S. F.; Yang, J. L.; Du, P. W. Chem. Commun. 2016, 52, 7164-7167. 2. Lu, D.P.; Zhuang, G. L.; Wu, H. T.; Wang, S.; Yang, S. F.; Du, P. W. Angew. Chem., Int. Ed. 2017, 56, 158-162. 3. Jia, H. X.; Zhuang, G. L.; Wang, J. Y.; Huang, Q.; Wu, Y. Y.; Zhou, Y.; Yang, S. F.; Du, P. W. submitted for publication, 2019. 4. Cui, S. S.; Zhuang, G. L.; Lu, D. P.; Jia, H. X.; Wang, Y.; Yang, S. F.; Du, P. W. Angew. Chem., Int. Ed. 2018, 57, 9330-9335. Figure 1

Corresponding relation between PL of multicrystalline silicon wafers and solar cell efficiency

Various market factors (e.g., anti-dumping and anti-bribery, subsidy retreat, etc.) have accelerated technology upgrading and cost efficiency of PV industry. Improving conversion efficiency is an effective way to reduce cost. Mainstream silicon manufacturers are intensifying research and development of next generation high-efficiency multicrystalline silicon wafer that is of higher efficiency. It is essential to obtain the cell efficiency parameters at silicon wafer-side. This work analyzes the relationship between PL image parameters of multicrystalline silicon measured by photoluminescence tester (PL) and the corresponding cell conversion efficiency, and the relationship between parameters of PL image and cells. Firstly, an analysis software is independently compiled to analyze the black silk and normalized intensity parameters of PL image, with the numerical results of the corresponding silicon wafers calculated. Selected high efficiency multicrystalline silicon bricks are cut into silicon wafers of 190 μm thickness, which are put to tests sequentially on the PL images of multicrystalline silicon wafers and then made into solar cells. The producing process of solar cells includes ordinary acid texturing, diffusion, removal of phosphosilicon silicon glass (PSG), plasma chemical vapor deposition (PECVD), screen printing, etc. Then cell efficiency and V oc parameters thereof are tested, with the correspondence between cell efficiency and parameters thereof and the PL parameters. The experimental data show that the tail is mainly affected by large grain boundaries and high impurity content. The correlation deviation of the cell efficiency, normalized strength of V oc and PL images, and black silk ratio parameters are greater than those of the middle section and the head. The black silk ratio is low, and its solar cells efficiency and V oc are high. The normalized strength of PL images is high, and its solar cells efficiency and V oc are high. But the normalized strength of PL images and V oc of cell have strong correlation with black silk ratio of PL images, and the normalized strength and black silk ratio of PL images have weak correlation with cell conversion efficiency. The reason is that material properties of PL photoluminescence test silicon are related to the corresponding cell V oc, and cell conversion efficiency is affected by many factors: texture, diffusion, coating processes, etc. In this paper, the expression of normalized strength of PL and cell V oc is deduced based on the semiconductor correlation principle. It is proved that the normalized strength of PL is strongly correlated with that of cell V oc in principle. The normalized strength of PL obtained by the analysis has the closest correlation with the quality of multicrystalline silicon wafers, which can be better used to guide the quality improvement of multicrystalline silicon wafers.

Evaluation of saw damage using diamond-coated wire in crystalline silicon solar cells by photoluminescence imaging

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future.

(Invited) Photoluminescnece Brightening in Single Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWNTs) are fundamentally interesting and technologically relevant materials with size tunable absorption and emission across a range of visible and near infrared wavelengths. However, several important aspects of their photophysical properties are not known in enough depth to predict how SWNTs will behave as part of larger integrated nanosystems. In particular, simple concepts such as the fundamental factors that affect photoluminescence efficiency (PL QY) are not well understood for SWNTs. We recently found that for DNA-wrapped SWNTS, the SWNT PL QY can be increased substantially in the presence of small amounts of mildly reducing molecules such as dithiothreitol (DTT) and Trolox. We will present comprehensive studies of the molecular-induced changes in PL from SWNTs suspended in several other commonly used surfactants. For example, upon addition of the reducing agents, sodium dodecyl sulfate (SDS) wrapped SWNTs showed a 4-fold PL intensity increase while sodium cholate (SC) wrapped SWNTs showed PL decrease by ~45%. Minimal change in PL was observed for SWNTs dispersed in sodium dodecylbenzene sulfonate (SDBS) and sodium deoxycholate (DOC). By using a state-of-the art NIR sensitive APD, we were able to acquire time resolved PL data from each sample. For SWNTs that were brightened (darkened), the non-radiative rate decreased (increased) and the radiative rate increased (decreased). Our preliminary conclusion is that adding the reductants causes a change in the molecular structure of the surfactant on the SWNT, which changes the local dielectric constant as well as the interaction of the exciton with the molecular orbitals of the surfactant. We will also present recent data on the PL brightening of individual SDS wrapped SWNTs, whereby we found the PL efficiency enhancement varied substantially among individual nanotubes, with some brightening by up to 6.5 times while others brightened by only 16%. Studies of NTs longer than the diffraction limit reveal the surprising finding that upon adding the reductants, the NTs brightened uniformly, as determined from the PL image. Since non-uniform brightening would result from consecutive interactions with individual point defects, the observation of uniform PL brightening is consistent with the interpretation that the reductants are causing changes in the local SWNT environment. Further, single step brightening across the entire NT followed by a constant, nonblinking PL level suggests the brightening effect could be due to as little as a single molecule interacting with the NT.

Injection-dependent Carrier Lifetime Analysis of Recombination Due to Boron-Oxygen Complexes in Wafers Passivated with Different Dielectrics by QSSPL and QSSPC

This paper compares the use of quasi-steady state photoluminescence (QSSPL) and photoconductance (QSSPC) measurements for injection-dependent carrier lifetime analysis of the state of boron-oxygen (B-O) complexes in boron-doped Czochralski wafers passivated with different dielectrics. Use of QSSPL measurements enabled effective carrier lifetime measurements over a larger range of injection levels than possible with QSSPC, potentially increasing the accuracy of estimates of the capture cross-section ratio of the deep-level B-O Shockley-Read Hall (SRH) defect. Although the capture cross-section ratios estimated using QSSPL (9.7 ± 1.7) and QSSPC (9.7 ± 1.9) for wafers symmetrically-passivated with silicon nitride and subsequently rapidly fired were very similar and close to the value of 9.3 reported by Rein et al. for the B-O defect, significant differences in the ratio and larger variances in the measurements within a group resulted for wafers with silicon nitride that was not annealed and wafers which were passivated with the thermal oxide. It is suggested the low-injection QSSPL measurements may introduce inaccuracies arising from the conduction of excited carriers via the diffused emitter away from the measurement area. This may suggest that there is little advantage in using QSSPL over the more commonly-used QSSPC measurements for these SRH analyses. Additionally, the study confirmed that stable regeneration of the effective carrier lifetime was only achieved when wafers were passivated with silicon nitride and underwent a rapid thermal anneal after deposition. If wafers were not rapidly thermally-annealed after silicon nitride deposition, then the recovery of effective lifetime observed with regeneration was not stable during a second light soak. Furthermore, the effective carrier lifetime of wafers passivated with a thermal oxide continued to decrease with light soaking, regeneration and a second light soaking with the appearance of “rings” in the PL images of oxide-passivated wafers as they underwent light soaking and regeneration highlighting the possible role of oxide precipitates in reactions occurring with light soaking and regeneration.

Defects Grouping and Characterizations of PL-Imaging Methods for 4H-SiC Epitaxial Layers

4H-SiC epitaxial wafers were prepared for the investigation of epitaxial stacking faults (SFs), for the purpose of classification and add to the epitaxial specification by PL-imaging analysis. Black colored SFs detected in PL colored images were focused, and investigated. Black SFs in the PL images were classified for two species, ones were correspond to the triangular defects, and the others were similar to the known SFs. Triangular defects were the killer defects for the I-V properties and the other black defects were not affected the I-V properties. Most of PL spectrums of triangular defects had the 538nm peak, and showed the 3C properties. Black defects undetectable as the surface defects (SDs) had 460, 480nm peak, differed from the reported typical 1-4SSFs spectrum. It seemed that these defects differed from the thickness of stacking layer and PL peak, whether the defects led to detectable/undetectable as the SDs. Thick stacking layers generated the triangular defects, and thin ones generated the PL-black defects undetectable as the surface analysis. Consequently, the black defects undetectable as the surface analysis (detected only for the PL-imaging analysis) has no use for add to the specification at the moment.

Localization of Excitons in Thin Core-Multi-Shell Quantum Well Tubes

ABSTRACTRecently, Fickenscher et al. [1] have shown that, in a core-multi-shell structure where a GaAs quantum well is embedded into an AlGaAs shell wrapped around a [111] oriented GaAs nanowire, the electron and hole ground states are strongly confined to the corners of the hexagonally symmetric quantum well. Thus this confinement defines quantum wires which run along the length of the nanowires along its corners. Here we review single nanowire photoluminescence measurements which show the significant confinement energy of the excitons. For well widths larger than 5 nm, optical transitions between electron and hole excited states can be seen in excitation spectra, while for widths less than 5 nm only the ground state optical transitions are observed. For well widths smaller than 5 nm, high resolution spatially resolved photoluminescence measurements show directly the appearance of localized states. Single nanowire spectra from the 4 nm QWT sample display ultranarrow emission lines on the high energy side of the luminescence band. Spatially-resolved PL images show that these quantum dots are localized randomly along the length of the wire.

Surface recombination parameters of interdigitated-back-contact silicon solar cells obtained by modeling luminescence images

Current losses at surfaces play a crucial role in the optimization of high-efficiency silicon solar cells. We present a new approach to characterize the surface recombination activity of interdigitated-back-contact (IBC) silicon solar cells by comparing experimental and simulated photoluminescence images (PL). The different recombination properties of the p- and n-doped regions of IBC cells in combination with the operating condition lead to contrast profiles in the PL image that vary with bias voltage. We achieve a good matching of experimental and simulated data for the investigated cells enabling the analysis of how sensitive the simulated contrast patterns are to changes in the surface recombination at the emitter, back- and front-surface-field and if a better matching of the experimental PL images is possible. Using these PL images in combination with simulations around the open circuit voltage Voc the determination of surface recombination velocities S and emitter saturation currents J0 on finished cells is made possible for the first time. This approach also opens a new path towards loss analysis of finished PERL, PERC, MWT and other silicon solar cells.

Unified Lifetime Metrology and Photoluminescence Imaging of Passivation Defects for Silicon PV

We have recently introduced an improved QSS-μPCD lifetime measurement with a strict quality of decay control technique. This enabled unified, parameter free determination of the decay lifetime and the steady-state lifetime over a broad steady-state injection range (up to about 30suns). Excellent correlation was found with Sinton QSSPC measurement. The advantage of spatially resolved μPCD was applied for wafer mapping. Emitter saturation current, J0, mapping was obtained directly from small perturbation decay lifetime using the Basore-Hansen procedure. The maps revealed commonly present passivation defects manifested as high J0 areas.In this work we report further improvement of the approach, especially regarding speed and resolution. Our research involved photoluminescence measurements on passivated test wafers in sequence with the QSS-μPCD unified lifetime measurement including J0. On selected sites the value of J0 was intentionally varied with corona charge induced field-effect. This enabled a unique PL calibration to J0 and other recombination parameters. Quantitative characteristics enabled us to compare PL procedures for the determination of J0 and to select a practical version for J0 imaging that uses direct J0 determination from the ratio of generation rate G to PL intensity. We have found that this J0 procedure correlates well with the commonly used Kane-Swanson method. In addition, it carries the practical advantages of needing only a single PL image with a straightforward calibration and relaxed requirements regarding injection range restriction.

Characterization of Oxidation-Induced Stacking Fault Rings in Cz Silicon: Photoluminescence Imaging and Visual Inspection After Wright etch

Oxidation-induced stacking fault rings in polished Cz silicon samples before and after thermal wet oxidation are investigated by use of photoluminescence imaging. Currently the standard procedure for OSF ring detection is to expose the samples to a toxic preferential etchant, e.g. a Wright solution, after a thermal oxidation. This solution primarily attacks the regions with stacking faults, allowing detection by visual inspection. Samples from the seed end of p-type Cz silicon ingots with resistivities of approximately 1Ohm-cm were measured by PL imaging before and after a thermal oxidation process. Subsequently, Wright-etching was performed on the oxidized samples to expose stacking faults. The lifetime variations in the PL images were correlated with the location of the rings in the preferentially etched surfaces, and good agreement was found. The results show that for this crystal pulling process, even the PL images of unpassivated polished samples can be used to detect the OSF ring location. The thermal oxidation at 1100°C enhanced the contrast between the OSF ring and the rest of the sample in the PL image.

Tip-Enhancement Effect on the PL of Localized Excitons in an InGaN Thin Film

Simultaneous measurements of the morphology, μ-PL, and tip-enhanced PL (TEPL) images of an InGaN thin film have been done. From a comparison between the μ-PL and TEPL images, the appearance of the bright spots in the TEPL image should be determined by the emission yield, permittivity of the sample and dipole orientation. The tip-enhancement effect on the temporal behaviour of the PL of the InGaN thin film has been measured. The temporal behaviour is altered by the tip-enhancement effect from a multi-exponential to single-exponential shape. This shows that the influx of the excitons from other potential minima to the luminescent energy level is suppressed by the existence of the gold-nano-particle attached to the tip.

APhen-functionalized nanoparticles–polymer fluorescent nanocomposites via ligand exchange and in situ bulk polymerization

Download options Please wait... Supplementary files Proton NMR spectra, PL images and DSC curves PDF (243K) Article information DOI https://doi.org/10.1039/B709566J Article type Paper Submitted 22 Jun 2007 Accepted 22 Aug 2007 First published 07 Sep 2007 Download Citation J. Mater. Chem., 2007,17, 4591-4597 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions APhen-functionalized nanoparticles–polymer fluorescent nanocomposites via ligand exchange and in situ bulk polymerization J. Gao, C. Lü, X. Lü and Y. Du, J. Mater. Chem., 2007, 17, 4591 DOI: 10.1039/B709566J To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Junfang Gao Changli Lü Xiaodan Lü Yaying Du