Organic–inorganic perovskite solar cells have experienced a remarkable development. In a short period of time power conversion efficiencies have jumped to values of more than 22%. However, the stability of these devices is an important subject. The stability of CH₃NH₃PbI₃ perovskite films is investigated using visible and ultraviolet light in oxygen atmosphere and in vacuum. Illumination in O₂ atmosphere results in a swift degradation. Oxygen acts as a catalyst decomposing methylammonium ions (CH₃NH₃⁺) into CH₃NH₂ and hydrogen. In vacuum, another degradation mechanism is observed. Prolonged illumination of the samples with photons from blue and UV light‐emitting diodes also results in dissociation of the methylammonium ion into CH₃NH₂ and hydrogen. In both cases the resulting molecules are highly mobile at room temperature and diffuse out of the samples. The light‐induced dissociation of CH₃NH₃⁺ is accompanied by the generation of localized defects in the band gap of the perovskite. Furthermore, the experimental data clearly show that the molecular orbitals of CH₃NH₃⁺ are not in resonance with the energy bands of the perovskite lattice.

Polycrystalline silicon (poly-Si) films were prepared by laser crystallization of amorphous silicon with various laser energy densities at substrate temperatures of 300 and 673 K. At $T_S=300\mathrm{}$ and 673 K poly-Si films with grain sizes of 1.5 and 1.0 μm were obtained at laser fluences of 540 and $505{\mathrm{m}\mathrm{J}/\mathrm{c}\mathrm{m}}^2,$ respectively. An increase of the grain size results in a decrease of the spin density due to a reduction of the grain-boundary volume. Moreover, the increase in substrate temperature resulted in a pronounced decrease of the spin density independent of the laser energy density. Defects are passivated by exposing the poly-Si films to monatomic H at 350 °C. This causes the spin density to decrease to a residual value of $\approx 9\times {10}^{16}{\mathrm{cm}}^{\mathrm{-}3}$ independent of substrate temperature and laser fluence.