Light trapping in thin film solar cells with sub-wavelength photonic crystal patterns
In this paper we investigate light-trapping in thin film crystalline silicon (c-Si) solar cells with shallow photonic crystal (PhC) front patterns. Coupling of light to the quasi-guided optical modes of the structures becomes a dominant feature when the thickness approaches the wavelength scale. Simple 1D and 2D patterns are investigated using a scattering matrix approach, and best results are compared with the Lambertian limit to light trapping. We show that light trapping can be enhanced by adding a controlled amount of disorder inside the PhC unit cell. We present some preliminary results about a Gaussian size-disorder in 1D structures, and we conclude that an advanced light-trapping design should rely on both order and disorder to maximize the absorption of sunlight.
Using the Z-scan technique, we study the nonlinear interaction of a dilute methanolic solution of chloro-aluminum phthalyocyanine with a ∼70 ns long train of laser pulses, each of 18 ps duration. The observations are explained by taking into account, in addition to the photoexcitation of a ground state molecule by a single pulse, thermal lensing and photoabsorption by an excited molecule (singlet or triplet) produced by previous pulses. A microscopic picture of the heating process in the solution is provided.