Light-and elevated Temperature-induced Degradation (LeTID) remains a challenge for the long-term stability of silicon-based solar cells. Despite numerous publications and studies on the subject, only a link with the hydrogen concentration in the silicon bulk has been established. However, the question remains as to how exactly hydrogen interacts with the defect or even forms part of it.In this study, highly sensitive resistivity measurements and photoluminescence/ photoconductance decay measurements are used to establish a precise correlation between the dominant hydrogen species (H2 and GaH) and the evolving defect concentration in fired Ga-doped silicon coated with an hydrogen-rich amorphous silicon nitride (SiN ������:H).The correlation appears to be linear in both species over the range investigated but the data imply that the defect concentration is proportional to H2. An investigation of the behavior of GaH during typical degradation conditions confirms that GaH pairs are hydrogen sinks and therefore do not contribute to the formation of LeTID defects. We therefore expect the hydrogen dimer to act as a precursor for LeTID.In addition, the indiffusion of H during the firing step from a SiN:H layer was investigated and a strong dependence on the peak temperature was found, whereas a weaker dependence on the cooling rate was observed.

Many studies suggest that hydrogen is an important factor for light and elevated temperature‐induced degradation (LeTID) in p‐type c‐Si solar cells. The exact mechanism of this defect is still unknown. Here, Ga‐doped Si wafers fired with an SiN x :H layer present were used to establish a correlation between the initial concentration of GaH pairs and H 2 dimers on one and the maximum defect density evolving during degradation on the other hand. Degradation of all samples is performed at constant excess charge carrier injection. The correlation to LeTID defect density is found to be linear in the case of [H 2 ], hence, a direct involvement of H 2 in the defect formation is expected. In contrast, the correlation between GaH pairs and defects is found to scale with the fraction of GaH on total hydrogen concentration. This fraction is not constant but rather decreases with an increase in total hydrogen concentration. In addition, changes in [GaH] and lifetime are examined under different degradation conditions with either fixed injection up to and temperatures up to 180 °C. Under these conditions, LeTID evolves but no dissociation of [GaH] takes place. The effective activation energy of LeTID defect formation is determined to be 0.76(17) eV.

Infrared absorption spectroscopy (FT-IR) done at room temperature can be successfully used for the quantification of boron-hydrogen pairs in crystalline silicon in the 10(14) to 10(15) cm(-3) range, where the detection limit is found to be in the low 1014 range. If the fraction of hydrogen that pairs with boron is known, it can be used to draw conclusions about the total hydrogen content in c-Si. Several measurements over the course of formation and dissociation of boron-hydrogen pairs can be obtained comparatively easily due to the lower effort at room temperature. Unlike other methods aiming for the unspecific change in net doping apparently caused by the formation of BH-pairs, the analysis of local vibrational mode (LVM) excitation is highly specific and allows to distinguish between BH-pair formation and other effects impacting hole concentration. Besides the analysis of LVM excitation, the interaction of infrared light with the free electron plasma (Drude's model) allows for a quantification of hole concentration as well, and thus allows for a direct cross-check with the LVM analysis.

The ability of hydrogen quantification in crystalline silicon in concentrations as low as 1014cm−3 becomes fairly important in regard to hydrogen-related degradation phenomena in silicon devices generally and solar cells particularly. The method presented here allows for direct boron–hydrogen pair quantification and, therefore, allows inference on total hydrogen content. Hydrogen-rich amorphous silicon nitride was deposited on stripes of boron-doped float-zone silicon (1 Ωcm), which were exposed to a rapid high temperature step to introduce relatively high amounts of hydrogen into the wafer. Infrared absorption spectra, which have been corrected for multiple reflection and free-carrier absorption, show absorption related to the boron–hydrogen stretching mode at ν~=1868cm−1 with varying strengths during formation and subsequent dissociation of boron–hydrogen pairs triggered by annealing in the dark at 220°C. Since the measurements were performed at room temperature, this method allows investigations with little effort and standard laboratory equipment. Furthermore, the change in free-carrier absorption (described by Drude’s theory) is used to derive the change in hole concentration concurring with the formation and dissociation of boron–hydrogen pairs. The latter is found to fairly match not only the changing strength in absorption of the stretching mode, but also the change in hole concentration obtained by highly sensitive resistivity measurements. The comparison of stretching mode absorption strength and change in resistivity allows for a calibration of specific absorption, yielding a calibration factor ABH. This calibration was performed with the absorption α [ABHα=(4.2±0.3)×1015cm−1] as well as with the quotient of absorption and wavenumber α/ν~ [ABHα/ν~=(7.8±0.6)×1018cm−2].

Hydrogen‐rich crystalline Si samples are produced by coating Ga‐doped Czochralski‐grown silicon wafers with SiN x :H and subsequent rapid thermal anneal. This procedure introduces H 2 dimers into the bulk, which enables the formation of gallium–hydrogen pairs (GaH). The change in pair concentration can be determined by change in resistivity, as pair formation consumes holes. During illumination at elevated temperature (180 °C), some of the previously formed GaH pairs dissociate into H and/or H 2 within hours. A subsequent anneal step forms the pairs again. If illumination is prolonged to days at 180 °C, a second dissociation phase occurs after which GaH pairs do not form again in the dark. Therefore, probably two processes are ongoing: a reversible (fast) one and an irreversible (slow) dissociation of GaH pairs in crystalline silicon. The fraction of dissociated pairs and rate of dissociation depend on temperature and excess charge carrier concentration. This suggests an electron‐driven, thermally activated back reaction into either H dimers or atomic hydrogen. An Arrhenius analysis reveals a possibly injection‐dependent activation energy of the reversible dissociation process in the range of 0.64–0.71 eV. Lifetime measurements reveal a drastic increase in effective defect density during the second decrease in pair concentration.

In crystalline silicon, atomic hydrogen released from hydrogen dimers forms acceptor–hydrogen pairs during annealing in the dark at elevated temperatures. In this study, the formation of boron–hydrogen (BH) and gallium–hydrogen (GaH) pairs in 1 Ω cm silicon is investigated at temperatures ranging from 140 to 220 °C. Acceptor–hydrogen concentrations in the low range are quantified by means of highly sensitive resistance measurements. GaH pairs are generally found to form faster than BH pairs. Arrhenius analysis shows a difference in activation energy (BH: 1.20 eV, GaH: 1.04 eV) while the trial frequency is the same ().

This study deals with the dynamics of the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon during a rapid high‐temperature treatment and subsequent dark annealing between 200 and 300 °C. Highly accurate resistivity measurements are used to detect BH pairs in chemically polished B‐doped float‐zone silicon. It is found that an unexpecteded high amount of hydrogen is present in the as‐purchased wafers. Hydrogen is initially mostly paired to boron but can be dissolved by a short high‐temperature firing step. If a firing step (530 °C) is applied to bare, unpassivated Si wafers, most of the initial BH pairs are dissolved, and hydrogen dimers () form. With increasing peak temperature, an increasing amount of hydrogen leaves the system, while the proportion of BH increases. Additional hydrogen can be introduced by firing a wafer passivated with plasma‐enhanced chemical vapor deposition (PECVD) H. A three‐state model shows a good agreement with the measured data for both bare and coated samples as well as for different annealing temperatures. With increasing dark annealing temperatures, the BH dynamics accelerates, whereas the maximum BH concentration reached decreases. For temperatures above 280 °C, significant changes in the reaction dynamics are observed.

We have studied potassium-intercalated bulk HfS$_2$ and HfSe$_2$ by combining transmission electron energy loss spectroscopy, angle-resolved photoemission spectroscopy and density functional theory calculations. Calculations of the formation energies and the evolution of the energies of the charge carrier plasmons as a function of the potassium content show that certain, low potassium concentrations $x$ are thermodynamically unstable. This leads to the coexistence of undoped and doped domains if the provided amount of the alkali metal is insufficient to saturate the whole crystal with the minimum thermodynamically stable potassium stoichiometry. Beyond this threshold concentration the domains disappear, while the alkali metal and charge carrier concentrations increase continuously upon further addition of potassium. At low intercalation levels, electron diffraction patterns indicate a significant degree of disorder in the crystal structure. The initial order in the out-of-plane direction is restored at high $x$ while the crystal layer thicknesses expand by 33-36%. Superstructures emerge parallel to the planes which we attribute to the distribution of the alkali metal rather than structural changes of the host materials. The in-plane lattice parameters change by not more than 1%. The introduction of potassium causes the formation of charge carrier plasmons. The observation of this semiconductor-to-metal transition is supported by calculations of the density of states (DOS) and band structures as well as angle-resolved photoemission spectroscopy. The calculated DOS hint at the presence of an almost ideal two-dimensional electron gas at the Fermi level for $x<0.6$. The plasmons exhibit quadratic momentum dispersions which is in agreement with the behavior expected for an ideal electron gas.