Silicon solar cells containing boron and oxygen are one of the most rapidly growing forms of electricity generation. However, they suffer from significant degradation during the initial stages of use. This problem has been studied for 40 years resulting in over 250 research publications. Despite this, there is no consensus regarding the microscopic nature of the defect reactions responsible. In this paper, we present compelling evidence of the mechanism of degradation. We observe, using deep level transient spectroscopy and photoluminescence, under the action of light or injected carriers, the conversion of a deep boron-di-oxygen-related donor state into a shallow acceptor which correlates with the change in the lifetime of minority carriers in the silicon. Using ab initio modeling, we propose structures of the BsO2 defect which match the experimental findings. We put forward the hypothesis that the dominant recombination process associated with the degradation is trap-assisted Auger recombination. This assignment is supported by the observation of above bandgap luminescence due to hot carriers resulting from the Auger process.

Results available in the literature on minority carrier trapping and light‐induced degradation (LID) effects in silicon materials containing boron and oxygen atoms are briefly reviewed. Special attention is paid to the phenomena associated with “deep” electron traps (J. A. Hornbeck and J. R. Haynes, Phys. Rev. 1955, 97, 311) and the recently reported results that have linked LID with the transformation of a defect consisting of a substitutional boron atom and an oxygen dimer (BsO2) from a configuration with a deep donor state into a recombination active configuration associated with a shallow acceptor state (M. Vaqueiro‐Contreras et al., J. Appl. Phys. 2019, 125, 185704). It is shown that the BsO2 complex is a defect with negative‐U properties, and it is responsible for minority carrier trapping and persistent photoconductivity in nondegraded Si:B+O samples and solar cells. It is argued that the “deep” electron traps observed by Hornbeck and Haynes are the precursors of the “slow” forming shallow acceptor defects, which are responsible for the dominant LID in boron‐doped Czochralski silicon (Cz‐Si) crystals. Both the deep and shallow defects are BsO2 complexes, transformations between charge states and atomic configurations of which account for the observed electron trapping and LID phenomena.

Abstract. Currently, there is a growing awareness that smoke produced during forest fires can expose individuals and populations to hazardous concentrations of air pollutants. Aiming to contribute to a better understanding of the air pollution phenomenon associated with forest fires, this paper presents and analyses the atmospheric emissions and air quality concentration measurements performed in the 2002 fire experiments at Gestosa, Central Portugal. Two vehicles were equipped with a meteorological station and air quality analysers that were turned on continuously to acquire concentrations of particulate matter, nitrogen oxides and carbon monoxide. Nitrogen and sulfur dioxides were measured using a grid of fixed passive samplers. Also, firefighters and research-team members used passive samplers during the experiments in order to estimate the human exposure to these pollutants. Measurements of volatile organic compound emissions, using Tedlar bags, were carried out. Results were analysed taking into account not only the concentration values but also the variables involved, such as the combustion phase and the meteorology, and identifying possible relationships between them. Despite the small size of the burning plots when compared to wildfires, the measured levels of pollutants were however considerable, indicating the effect of these experiments on the local air quality and stressing the serious levels of air pollution that can be expected during wildfires.Additional keywords: air quality; forest fire emissions.

It is widely believed that the light induced degradation of crystalline silicon solar cells is due to the formation of a B s O 2i recombination center created by the optically excited migration of the oxygen dimer ͑charge-state-driven motion͒. In this letter the concentration dependence of the neutral state of O 2i on ͓O i ͔ in p-and n-type Cz-Si has been determined using infrared absorption. A systematic search for the absorption signature of the dimer in the doubly positively charged state has been unsuccessful. These data strongly suggest that charge-state-driven motion ͑Bourgoin-Corbett mechanism͒ of the oxygen dimer cannot occur in typical solar silicon and hence bring into question the accepted degradation mechanism.

It has been acknowledged for over 50 years that treatments with hydrogen can improve silicon semiconductor devices. In recent years, these have been used to an advantage in silicon solar cells reducing the loss of photo‐generated carriers at the silicon surface or at the silicon interface with dielectrics. However, we have found that in some types of silicon the in‐diffusion of hydrogen can result in the formation of powerful recombination centers composed of carbon, oxygen, and hydrogen which reduce the carrier lifetime and ultimately the efficiency of solar cells made from such material.