Funding was provided by the State of Lower Saxony.
D.M. is supported by an Australian Research Council QEII
Fellowship.

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Generation and annihilation of boron–oxygen-related recombination centers in compensated p- and n-type silicon

Theoretical calculations reveal that the quality of an aluminum-back-surface field (BSF) in a silicon solar cell can be improved by either increasing the thickness of the deposited aluminum (Al), peak alloying temperature, or both. However, this study shows that there is a critical temperature for a given screen-printed Al thickness, above which the BSF quality begins to degrade because of nonuniformity triggered by the agglomeration of Al-Si melt in combination with the bandgap narrowing resulting from the high doping effect in the agglomerated regions. It is found that this critical temperature decreases with the increase in the thickness of the deposited Al layer and, therefore, limits the quality and thickness of the Al-BSF that can be achieved before degradation sets in. This nonuniformity of Al-BSF is observed in the form of scattered Al bumps with thick and thin BSF regions. A combination of experimental results and model calculations is used to provide improved understanding and guidelines for choosing the optimal combination of Al thickness and alloying temperature.

Factors Limiting the Formation of Uniform and Thick Aluminum–Back-Surface Field and Its Potential

This article is the second article in a three-part series dedicated to reviewing each process step in crystalline silicon (c-Si) photovoltaic (PV) module manufacturing process: feedstock and wafering, cell fabrication, and module manufacturing. The goal of these papers is to identify relevant metrology techniques that can be utilized to improve the quality and durability of the final product. The focus of this article is on the cell fabrication process. In this review, the fabrication of c-Si PV cells is divided into four steps: (1) wet chemical processes; (2) emitter formation; (3) anti-reflection coating (ARC) and passivation deposition; and (4) metallization. Each of these processing steps can impact the final reliability and durability of PV modules deployed in the field, and here the failure modes and degradation mechanisms induced during cell manufacturing are explored. Additionally, a literature review of relevant measurement techniques aimed at reducing or eliminating the probability of such failures occurring is presented along with an assessment of potential gaps wherein the PV community could benefit from new research and demonstration efforts.

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Manufacturing metrology for c-Si module reliability and durability Part III: Module manufacturing

This paper reports the fabrication method and humidity sensing performances of zinc oxide nanorods (ZONRs) and chitosan self-assembled monolayers (SAMs) modified ZONRs patterned piezoresistive silicon MEMS microcantilevers. The self-actuating and self-sensing microcantilevers were fabricated using standard silicon wafers and bulk-micromachining techniques; a p-diffused heating resistor was patterned at the clamped end of the microcantilever as the self-actuator. Moreover, the resonant frequency shift induced by the mass change of adsorbed water on the hybrid sensing nanostructure can be read-out directly by a p-diffused full Wheatstone bridge. Aligned high-surface-to-volume-ratio ZONRs were selectively deposited on the microcantilever as the sensing material using a simple low-temperature chemical-bath deposition (CBD) process based on a DC sputtering/annealing ZnO seed-layer. In addition, for comparison, a low-cost seed-layer method using aqueous chemical growth (ACG) method was also applied to deposit ZONRs. Furthermore, chitosan SAMs were self-assembled on the ZONRs, yielding a microcantilever-based gravimetric relative humidity (RH) sensor with good stability and repeatability (± 0.06%RH over 90 min), high sensitivity (ZONRs: 4.4 ppm/%RH; chitosan-SAMs@ZONRs: 16.9 ppm/%RH), and low hysteresis error (2.1%RH).

Fabrication of ZnO nanorods and Chitosan@ZnO nanorods on MEMS piezoresistive self-actuating silicon microcantilever for humidity sensing

The thermal stability of amorphous silicon/silicon nitride double layer surface passivation of p-type and n+-type crystalline surfaces is investigated for different deposition temperatures of the silicon nitride capping layer. An increase from 300to400°C results in a significant improvement of the thermal stability of the surface passivation. The minimum surface recombination velocity achieved on p-type (1.5Ωcm) silicon wafers is 0.75±0.6cm∕s and remains at 10±0.5cm∕s after 30min annealing at 500°C.

Thermal stability of amorphous silicon/silicon nitride stacks for passivating crystalline silicon solar cells

The electrochemical capacitance-voltage (ECV) technique was used to measure the carrier concentration profiles in Si Using the conventional parallel-equivalent circuit model of the Schottky junction to describe the electrolyte-silicon barrier we found excellent agreement between ECV and four-point probe analyses within ±10 to 20% for bulk Si uniformly doped p- and n-type from 10 12 to 10 18 cm -3  In this concentration range accuracy limits are determined mainly by the precise measurement of the area of the electrolyte-Si contact For the anodic etching of Si, a constant effective dissolution valence of z=37 was used throughout the measurements Investigations with isotype and anisotype doping transitions were performed employing ECV and other profiling techniques for comparison

D. Krüger

Papers

Doping Profile Analysis in Si by Electrochemical Capacitance‐Voltage Measurements