ORCID Profile
0000-0002-9373-2213
Current Organisation
University of New South Wales
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Publisher: Elsevier BV
Date: 2014
Publisher: AIP Publishing
Date: 09-01-2019
DOI: 10.1063/1.5063849
Abstract: A p+-i-n+ self-cooled light-emitting diode with type-II band offset is numerically simulated in one-dimension to examine the underlying cooling/heating mechanisms. The Peltier effect is confirmed to be the dominant cooling mechanism under forward bias, even when the carriers are injected without an energy barrier. Meanwhile, Joule heating in the active layer is identified as the main heating mechanism for bandgaps below 0.52 eV under an ultra-low forward bias. In contrast to non-radiative recombination, electroluminescence itself is found to be a cooling mechanism, producing most photons above the bandgap of the active layer. However, this effect only becomes noticeable under an ultra-low bias in very small bandgap materials. While it is desirable to inject more carriers to leverage larger band offsets for a higher cooling power, Joule heating limits the maximum cooling power achievable. With small band offsets (& .21 eV), a reverse bias instead of a forward bias may become the best cooling condition, where non-radiative generation processes are discovered to be the dominant cooling mechanisms.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2017
Publisher: Wiley
Date: 04-08-2017
Publisher: AIP Publishing
Date: 04-09-2013
DOI: 10.1063/1.4819970
Abstract: In this work, we demonstrate that by using H2O based thermal atomic layer deposited (ALD) Al2O3 films, excellent passivation (emitter saturation current density of ∼28 fA/cm2) on industrial highly boron p+-doped silicon emitters (sheet resistance of ∼62 Ω/sq) can be achieved. The surface passivation of the Al2O3 film is activated by a fast industrial high-temperature firing step identical to the one used for screen printed contact formation. Deposition temperatures in the range of 100-300 °C and peak firing temperatures of ∼800 °C (set temperature) are investigated, using commercial-grade 5″ Cz silicon wafers (∼5 Ω cm n-type). It is found that the level of surface passivation after activation is excellent for the whole investigated deposition temperature range. These results are explained by advanced computer simulations indicating that the obtained emitter saturation current densities are quite close to their intrinsic limit value where the emitter saturation current is solely ruled by Auger recombination. The process developed is industrially relevant and robust.
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 11-2017
Publisher: WIP
Date: 2012
Publisher: IOP Publishing
Date: 04-09-2013
Publisher: AIP Publishing
Date: 15-10-2021
DOI: 10.1063/5.0061483
Abstract: Organic–inorganic metal halide perovskite solar cells represent the fastest advancing solar cell technology in terms of energy conversion efficiency improvement, as seen in the last decade. This has become a promising technology for next-generation, low-cost, high-efficiency photovoltaics including multi-junction tandem cell concepts. Double-junction tandem cells have much higher efficiency limits of 45%, beyond the Shockley–Queisser limits for a single-junction solar cell. In this review, recent progress with the perovskite tandem solar cells is highlighted, in particular, with 2-terminal perovskite–Si, perovskite–CIGS [where CIGS = Cu(In,Ga)(S,Se)2], perovskite–organic photovoltaic, perovskite–perovskite, and 3-junction-perovskite tandems. The opportunity and challenges of two-terminal monolithic perovskite tandems are discussed including a roadmap of strategies for further improving their efficiencies.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2013
Publisher: AIP Publishing
Date: 11-11-2014
DOI: 10.1063/1.4901242
Abstract: Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime s les. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured s les. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boron diffusion recipes on planar s les. The established parameters are subsequently used to simulate the boron diffusion process on textured s les. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured s les is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured s les to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured s les. The differences between planar and textured s les are discussed.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2010
Publisher: AIP Publishing
Date: 07-2015
DOI: 10.1063/1.4926809
Abstract: This paper presents a three-dimensional numerical analysis of homojunction/heterojunction hybrid silicon wafer solar cells, featuring front-side full-area diffused homojunction contacts and rear-side heterojunction point contacts. Their device performance is compared with conventional full-area heterojunction solar cells as well as conventional diffused solar cells featuring locally diffused rear point contacts, for both front-emitter and rear-emitter configurations. A consistent set of simulation input parameters is obtained by calibrating the simulation program with intensity dependent lifetime measurements of the passivated regions and the contact regions of the various types of solar cells. We show that the best efficiency is obtained when a-Si:H is used for rear-side heterojunction point-contact formation. An optimization of the rear contact area fraction is required to balance between the gains in current and voltage and the loss in fill factor with shrinking rear contact area fraction. However, the corresponding optimal range for the rear-contact area fraction is found to be quite large (e.g. 20-60 % for hybrid front-emitter cells). Hybrid rear-emitter cells show a faster drop in the fill factor with decreasing rear contact area fraction compared to front-emitter cells, stemming from a higher series resistance contribution of the rear-side a-Si:H(p+) emitter compared to the rear-side a-Si:H(n+) back surface field layer. Overall, we show that hybrid silicon solar cells in a front-emitter configuration can outperform conventional heterojunction silicon solar cells as well as diffused solar cells with rear-side locally diffused point contacts.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2007
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2009
Publisher: Elsevier BV
Date: 02-2017
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2009
Publisher: AIP Publishing
Date: 25-02-2015
DOI: 10.1063/1.4913451
Abstract: The effective minority carrier lifetime of p-type silicon wafers passivated by silicon nitride and of n-type silicon wafers passivated by aluminium oxide often decreases significantly as the excess carrier concentration decreases. Several theories have been postulated to explain this effect. The main ones are asymmetric carrier lifetimes, high recombination within a surface damage region, and edge recombination. As in some cases, the effective lifetime measurements can be fitted quite well by all these effects, it is challenging to determine the main cause for the suppressed performance at low illumination. This is partly due to the fact that no study has yet included a sufficiently large set of wafers and advanced modelling to examine all these theories. The aim of this study is to determine the most likely theory based on a set of undiffused p- and n-type wafers of different sizes, passivated with both silicon nitride and aluminium oxide. Quasi-steady-state photoluminescence measurements were used in order to investigate effective lifetime at very low carrier densities, without artifact effects that commonly limit photoconductance-based measurements. Advanced modelling using Sentaurus was used to investigate the impact of different parameters—such as the fixed charge within the dielectric—on the recombination at the edge and within the surface damage region. These models were then used to simulate the measurement results. It is shown that asymmetrical surface lifetime cannot explain the observed reduction when the dielectric is highly charged (either positively or negatively). It is also shown that although edge recombination influences the effective lifetime at low excess carrier concentration, it alone cannot explain the effective lifetime reduction. It is therefore concluded that the presence of a surface damage region is the more likely explanation for the effective lifetime decrease of the studied wafers.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2015
Publisher: AIP Publishing
Date: 09-2012
DOI: 10.1063/1.4749572
Abstract: A strong injection level dependence of the effective minority carrier lifetime (τeff) is typically measured at low injection levels for undiffused crystalline silicon (c-Si) wafers symmetrically passivated by a highly charged dielectric film. However, this phenomenon is not yet well understood. In this work, we concentrate on two of those possible physical mechanisms to reproduce measured τeff data of c-Si wafers symmetrically passivated by atomic layer deposited Al2O3. The first assumes the existence of a defective region close to the c-Si surface. The second assumes asymmetric electron and hole lifetimes in the bulk. Both explanations result in an adequate reproduction of the injection dependent τeff found for both n- and p-type c-Si wafers. However, modeling also predicts a distinctly different injection dependence of τeff for the two suggested mechanisms if the polarity of the effective surface charge is inverted. We test this prediction by experimentally inverting the polarity of the effective surface charge using corona charges. From the experiments and simulations, it is concluded that surface damage is the most likely cause of the significant reduction of τeff at low injection levels.
Publisher: Springer Science and Business Media LLC
Date: 29-05-2014
No related grants have been discovered for Fajun Ma.