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.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.New experimental and theoretical results on the silicon diinterstitial (I 2 ) and its interactions with oxygen and carbon impurity atoms in Si crystals are reported. Electronic structure calculations indicate that I 2 has an acceptor and a donor level in the gap, which are close to the conduction and the valence band edges, respectively. Experimental results, which support the theoretically predicted high mobility of I 2 , are discussed. It is argued that mobile I 2 can be trapped by oxygen and carbon impurities. The I 2 O center has a donor level at E v þ0.09 eV. Two absorption bands at 936 and 929 cm À1 are assigned to the local vibrational modes of the I 2 O defect in the neutral and positively charged states, respectively. The binding energy of I 2 O relative to the separated I 2 and O i species is 0.22 eV. The disappearance of the I 2 O complex upon thermal annealing occurs in the temperature range 50-100 8C and is accompanied by the introduction of another defect, which gives rise to two hole emission signals from energy levels at E v þ0.54 and E v þ0.45 eV. It is argued that these levels are related to a complex consisting of interstitial carbon and interstitial silicon atoms (C i I). The stable configurations of the C i I pair have been found.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.In the present work, we report local vibrational mode (LVM) related absorption lines which are assigned to the complex incorporating interstitial boron and interstitial oxygen atoms (B i O i ), a possible precursor of the center responsible for lightinduced degradation (LID) in solar cells produced from boron-doped oxygen-rich silicon. Fourier transform infrared absorption (IR) spectroscopy was used for detection and analysis of absorption lines due to defects which were created in boron-doped Czochralski-grown Si samples by irradiation with 6 or 10 MeV electrons at room temperature. Changes in the IR absorption spectra upon isochronal annealing of the irradiated samples in the temperature range 75-225 8C have also been monitored. A set of previously unreported LVM lines with the same formation and elimination behavior has been studied. The most intense lines of the set are found to be at 991, 721, and 550 cm À1 . On the basis of an analysis of changes in intensity of the lines with the concentrations of impurities in the silicon and on the similarity of their annealing features with those for the DLTS signal due to the B i O i center, it is argued that the lines are related to the LVMs of this defect. The positions of the lines have been compared with the previously reported LVMs derived from ab initio modeling calculations for different configurations of the B i O i complex. A configuration having calculated LVMs close to those determined experimentally has been found and the origins of the modes are discussed.

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