Light trapping is an important technique in increasing the efficiency of solar cells. Inverse optimization is a systematic numerical approach that allows us to find the limits of light trapping more efficiently. It is an alternative to exhaustive search simulations or experimental measurements. In this work, we use inverse optimization to study light trapping in thin film amorphous silicon cells textured by periodic patterns of metallic surface grating. We use a finite set of Haar wavelets to describe a general form of grating structure composed of multiple rectangular nano-strips. We use global simulated annealing optimization to find the coefficients of the wavelets basis for optimal absorption enhancement in thin film silicon. The motivation for choosing wavelet basis (vis-a-vis other orthonormal bases such as Fourier) is the feasibility of fabricating the resulting nano-structures. The resulting improvement in the number of absorbed photons is around 130% for wavelength range of 300–700nm, which is significantly better than the previous results using simple front surface nano-strips. In addition, we use statistical analysis to evaluate the sensitivity of the characteristics of the resulting structure to numerical uncertainties.

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