Light and elevated temperature induced degradation (LeTID) of high-performance (HP) multicrystalline silicon (mc-Si) is a problem which affects manufacturers of mc-Si PERC cells and its root cause is ...still being debated. Several hypotheses for the root cause have been suggested which involve metal precipitates, and/or the introduction of hydrogen. Some of these hypotheses may be tested by controlled LeTID experiments in different parts of the mc-Si ingot, which are known to have different grain sizes, dislocation densities, doping and a large change in some of the impurities present. Limited publications are available showing the LeTID behavior of mc-Si in different parts of the ingot. In this study we show that the degradation rate and extent of LeTID during accelerated processing is not majorly influenced by the wafer's origin within the ingot which is studied here. We also confirm that the firing temperature before the degradation process has a large impact on the degradation extent, and this relationship is not significantly affected by the wafer's origin in the ingot, either.
Intrinsic amorphous silicon provides excellent surface passivation on crystalline silicon. It has previously been shown, that carriers that are photo generated in the amorphous silicon can be ...efficiently electronically injected into the crystalline silicon. A method to quantify the efficiency of such carrier injection using the spectral response of photoluminescence has recently been demonstrated. As this is a contactless method, it can be applied to incomplete device structures. Here we, use this technique to measure partially processed heterojunction devices with different capping layers to quantify their impact on the carrier injection efficiency. Silicon nitride capping on amorphous silicon is shown to have minimum impact on the high carrier injection efficiency of the amorphous layer whereas phosphorus doped amorphous capping layers on the other hand were seen to have a strong effect on the carrier injection efficiency.
The influence of multicrystalline silicon ingot properties on the final performance of mass produced PERC solar cells is an area of great interest in PV manufacturing. An ability to better understand ...this relationship can result in more rapid and targeted development of the ingot-growing process conditions. Likewise, a better understanding of the impact of input wafer material can lead to improved understanding and outcomes for the device manufacturing sequence. The present study uses a set of ingot level metrology data that is paired with final device performance data. This data set has been previously studied for relationships related to open circuit voltage and short circuit current. The present study completes the association with device efficiency by focusing on the relationships to the final fill factor of the device. The analysis shows that the wafer resistivity has a strong influence on the series resistance of the final device. The presence of defects within the device has a surprising influence on this relationship (which might be explained by systematic errors in the in-line measurements of the series resistance). A new method is developed for parameterizing the enhanced recombination in the device, and relationships to the ingot level lifetime data and the as-cut wafer defect level are demonstrated. The study concludes with a discussion on the implications of the results and the opportunity for further study.
We investigate the limitations of two-photon time resolved photoluminescence to measure the bulk lifetime of different semiconductor materials used for photovoltaic applicationsThe alternating ...difference implicit finite-difference time-domain method was employed to simulate the carrier kinetics, following the localized generation of carriers by an ultra-fast laser pulse. Three hypothetical materials were modelled: direct bandgap material for thin-film applications (such as CZTS), direct band-gap for thick--film applications (such as GaAs), and indirect band-gap thick material (such as silicon). It was found that the effective lifetime of the direct band-gap materials remains within an order of magnitude of the bulk lifetime, even for surface recombination velocities up to 10 7 cm/s. For the indirect band-gap material, the bulk lifetime is inaccessible, at even moderate surface recombination velocities, due to the combination of high bulk lifetime and high diffusivity. This is the firststudy that highlights the limit of the two-photon time-resolved method for silicon applications.
Temperature-dependent lifetime spectroscopy is a well-established characterization technique used to determine the energy level of recombination centers (defects). The determination of the energy ...level is performed through analysis of measured lifetime over a range of temperatures at a fixed excess carrier concentration. In recent years, photoluminescence imaging has been extensively used for spatially resolved measurements of many electronic material and device parameters of silicon wafers and silicon solar cells. However, photoluminescence imaging at elevated temperatures has not been widely used. This study presents initial results of photoluminescence imaging measurements taken at high temperatures.
High-efficiency silicon light emitting diodes Green, Martin A.; Zhao, Jianhua; Wang, Aihua ...
Physica. E, Low-dimensional systems & nanostructures,
03/2003, Volume:
16, Issue:
3
Journal Article
Peer reviewed
Silicon has been regarded as a notoriously poor emitter of light fundamentally due to its indirect bandgap. However, as an elemental rather than a compound semiconductor, it has the advantage of ...fewer background defects as well as well-developed approaches to interface passivation. By minimising parasitic optical absorption and non-radiative bulk and surface recombination, and by enhancing the effective optical photon generation volume, respectable silicon light emission efficiencies are demonstrated. These are within the range of direct gap III–V semiconductors and higher than any at low powered densities. Possible applications are also discussed.
In this paper, we present studies of plasma-enhanced chemical vapor deposited silicon nitride in which photoluminescence imaging was used to characterize our deposition process. A showcase of ...different processing issues such as equipment design, processing conditions, and manual handling is presented. We also demonstrate how photoluminescence imaging can be particularly useful for process monitoring, diagnoses, and development. An increase in implied V oc of up to 25 mV was achieved through the use of PL imaging as a diagnostic tool
Developed by researchers at the University of New South Wales (UNSW) in Sydney, the patented technology enables PL images to be measured with acquisition times less than 1 s,1 Only a few years after ...its introduction, research institutes and silicon wafer and solar cell manufacturers worldwide use commercial PL imaging equipment, which is offered by BT Imaging, a UNSW spin-off company.2 How it works In PL imaging of silicon samples, the entire surface of the sample - typically 156 ? 156 mm - is illuminated homogeneously. Systematic PL imaging inspection of silicon wafers and automatic assessment of metrics derived using image-analysis methods allow cell performance to be predicted at the start of cell manufacturing - a unique opportunity enabled for the first time by fast PL imaging.5, 6> 7 Analyzing PL on silicon wafers from bottom to top of a silicon brick also enables the 3D distribution of defects within a brick to be measured, valuable information for gaining understanding and better control of the crystallization process.
