Ziv Hameiri

18.7% efficient laser-doped solar cell on p-type Czochralski silicon

The use of laser doping in solar cell fabrication has received increased attention in recent years, especially due to its ability to form a selective emitter without subjecting the wafer to prolonged high-temperature processes. At the University of New South Wales, a laser doping method was developed that combines the formation of the selective emitter with a self-aligned metallization pattern. This letter reports 18.7% efficient laser-doped solar cells, fabricated on large area commercial-grade p-type Czochralski silicon, and analyzes the loss mechanisms.

Inter-laboratory study of eddy-current measurement of excess-carrier recombination lifetime

Excess-carrier recombination lifetime is a key parameter in silicon solar cell design and production. With the vast international use and recent standardization (SEMI PV13) of eddy-current wafer and brick silicon lifetime test instruments, it is important to quantify the inter- and intra-laboratory repeatability. This paper presents results of an international inter-laboratory study conducted with 24 participants to determine the precision of the SEMI PV13 eddy-current carrier lifetime measurement test method. Overall, the carrier recombination lifetime between-laboratory reproducibility was found to be within ±11% for quasi-steady-state (QSS) mode and ±8% for transient mode for wafer samples and within ±4% for bulk samples.

Rear junction laser doped solar cells on CZ n-type silicon

N-type silicon (Si) has been shown to have generally higher bulk lifetimes and far better post illumination performance stability compared to boron doped p-type materials of similar crystallographic quality. In particular, the high minority carrier diffusion lengths in n-type wafers makes the rear emitter n+np+ structure an attractive option, especially when incorporated with screen printing as a simple and cost effective way to create an Al-alloyed junction on the back surface. However, when screen printing is used to apply the front contacts, its wide metal lines and its requirement for a heavy Phosphorus-doped front surface significantly reduces the performance of this simple device with the latter limiting the blue wavelength response and surface passivation quality. Recently, the laser doping process has been shown capable of overcoming these major drawbacks due to its ability to produce a selective emitter. In this present work, an innovative application of the laser doping process in the fabrication of such rear Al-alloyed emitter n+np+ device enables an excellent energy conversion efficiency of 18.2% to be achieved on commercial grade n-type CZ wafers (148.6cm2).

Deposition temperature independent excellent passivation of highly boron doped silicon emitters by thermal atomic layer deposited Al2O3

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 recombinatio...

Recombination parameters of lifetime-limiting carrier-induced defects in multicrystalline silicon for solar cells

In p-type multicrystalline silicon solar cells, carrier-induced degradation (CID) can cause up to 10% relative reduction in conversion efficiency. Although, a great concern has been drawn on this degradation in the photovoltaic community, the nature of this degradation is still yet unknown. In this contribution, the recombination parameters of the responsible defect causing this degradation are extracted via temperature and injection dependent lifetime spectroscopy. Three wafers from three different ingots were processed into cell precursor and lifetime structures for the study. Similar defect recombination parameters were obtained for all samples. Two candidates for the defect energy level were identified: Et − Ei = −(0.32 ± 0.05) eV or Et − Ei = (0.21 ± 0.05) eV in the lower and upper bandgap halves, respectively. The capture cross section ratios were found to be k = 56 ± 23 or k = 49 ± 21 for the lower and upper bandgap halves, respectively. Contrary to previous studies, these parameters have been extr...

Spatially resolved electrical parameters of silicon wafers and solar cells by contactless photoluminescence imaging

A contactless method to extract spatially resolved electrical parameters of silicon wafers and silicon solar cells is introduced. The method is based on photoluminescence imaging and can be applied throughout the solar cell fabrication process, even before junction formation. To validate the method, the parameters obtained by it are compared to the ones obtained by the well-established Suns-Voc measurement. Good agreement is obtained.

Imaging the local ideality factor by contactless photoluminescence measurement

A contactless method to image the local ideality factor of silicon wafers and silicon solar cells is introduced. The method is based on photoluminescence imaging and can be applied throughout the solar cell fabrication process, even before junction formation. The local ideality factor measured by the proposed method is found to be in good agreement with that measured by Suns-Voc. Examples of its application are given for fully and partially fabricated solar cells.

Carrier-Induced Degradation in Multicrystalline Silicon: Dependence on the Silicon Nitride Passivation Layer and Hydrogen Released During Firing

Carrier-induced degradation (CID) of multicrystalline silicon (mc-Si) solar cells has been receiving significant attention; however, despite this increasing interest, the defect (or defects) responsible for this degradation has not been determined yet. Previous studies have shown that the surface passivation layer and the firing temperature have a significant impact on the rate and extent of this degradation. In this paper, we further study this impact through an investigation of the CID behavior of the mc-Si wafers passivated with six different silicon nitride layers, each fired at four different peak temperatures. At low firing temperatures, no significant difference in the CID was identified between the samples with different passivation layers; however, a large range of degradation extents was observed at higher firing temperatures. Using Fourier transform infrared spectroscopy, a correlation was found between the degradation extent and the amount of hydrogen released from the dielectric during firing. We verified that no degradation of the surface passivation quality occurred, indicating that the degradation is primarily associated with a bulk defect.

Dielectric Charge Tailoring in PECVD SiO

State-of-the-art surface passivation results are obtained on undiffused p-type commercial-grade Czochralski Si wafers with effective surface recombination velocity S_eff values of ~8 cm/s and implied open-circuit voltage iV_oc values of up to 715 mV with an industrially fired dielectric stack of silicon oxide and silicon nitride (SiO_x/SiN_x) deposited in an industrial inline plasma-enhanced chemical vapor deposition reactor. We are able to controllably vary the total positive charge density Q_total in the stack by more than one order of magnitude (10¹¹-10¹² cm^-2) with no impact on midgap interface state density D_{it,m idgap} (5 × 10¹¹ eV^-1· cm^-2) by altering the deposition temperature of the SiO_x layer in the stack. We show experimentally that, for inversion conditions, S_eff scales with the inverse square of the charge density 1/Q²_total, which is in good agreement with theory. Based on the measured injection-level-dependent minority carrier lifetimes and the total positive charge densities, it is shown that films with higher positive charge density have higher 1-sun Voc and fill factor (FF) potential. Large-area alloyed aluminum local back surface field solar cells confirmed this by showing higher conversion efficiency by 0.17% absolute due to improved cell V_oc and FF of the solar cells featuring a SiO_x/SiN_x stack with a higher Q_total.

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Abstract Luminescence imaging is a versatile characterisation technique used for a broad range of research and industrial applications, particularly for the field of photovoltaics where photoluminescence and electroluminescence imaging is routinely carried out for materials analysis and quality control. Luminescence imaging can reveal a wealth of material information, as detailed in extensive literature, yet these techniques are often only used qualitatively instead of being utilised to their full potential. Part of the reason for this is the time and effort required for image processing and analysis in order to convert image data to more meaningful results. In this work, a custom built, Matlab based software suite is presented which aims to dramatically simplify luminescence image processing and analysis. The suite includes four individual programs which can be used in isolation or in conjunction to achieve a broad array of functionality, including but not limited to, point spread function determination and deconvolution, automated sample extraction, image alignment and comparison, minority carrier lifetime calibration and iron impurity concentration mapping. Program summary Program title: LumiTools Program Files doi: http://dx.doi.org/10.17632/7nd34fbwfg.1 Licensing provisions: Creative Commons by 4.0 (CC by 4.0) Programming language: Matlab Nature of problem: Data acquired using the technique of luminescence imaging require unique corrections and processing in order to convert the qualitative image into more meaningful, quantitative results. Such processing is often non-trivial and can present a barrier to research. Solution method: The LumiTools package provides a broad array of common functionality required for the processing and analysis of luminescence images. Several tools are available to allow processing for various applications and each tool has been developed with a simple to use graphical user interface.