Collaborative Research: Integrated Optoelectronic Optimization of Thin-Film Solar Cells with Light-Trapping Structures

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Although recent years have seen a rapid drop in the cost of standard thick crystalline-silicon solar-cells, small-scale photovoltaic generators of energy (solar cells) must become ubiquitous for human progress to become truly unconstrained by energy economics. Using an integrated optoelectronic computer model developed under a previous NSF grant, the Principal Investigators (PIs), have shown that thin-film solar cells containing absorber layers with optimally graded electrical properties can have theoretical electrical generation efficiencies of over 34%, a large increase over previous designs and competitive with heavier standard solar cells. Once manufactured, such solar cells could be incorporated in wearables, textiles, car roofs, etc, and deployed with less infrastructure than current crystalline-silicon devices. Further improvement to the design requires the incorporation of light-trapping structures, such as antireflection coatings to improve the absorption of light, that are jointly optimized with the composition of the electricity generating layers by grading the bandgap parameters. In addition, simplified designs better suited to manufacture need to be investigated. These additional steps require mathematical improvement to the optoelectronic model, and the investigation of several new combinations of materials with simplified bandgap grading. This is a multidisciplinary project with two major goals: mathematical and physical. The mathematical goal is to enhance the integrated optoelectronic model by (i) using modern methods of numerical analysis to improve the efficiency of the photonics solver, and (ii) improving the robustness and reliability of the Hybridizable Discontinuous Galerkin method (HDG) finite element method applied to the drift-diffusion system for charged-particle transport. In particular, the PIs will analyze and implement a completely new approach by hybridizing the rigorous coupled-wave approach (RCWA) with the C method for solving Maxwell’s equations in 2D and 3D. As the HDG solver for the drift-diffusion problem needs improved robustness and efficiency to handle layered designs more suitable for manufacturing, the PIs will analyze and implement a dual-weighted residual approach to a posteriori error estimation of the total current and investigate the use of Anderson acceleration for the non-linear solver. It is expected that the software developed on this project will be useful to the wider photonics community. The physical goal is to use the newly developed fast and adaptive solver so that the improved algorithms can be used to simultaneously optimize light-trapping structures and bandgap grading parameters. The light-trapping structures will include multilayered antireflection coatings, nanocone arrays, and combinations of both. The PIs expect to spur the development of colored solar cells to power miniature electronic and optical devices on clothes, car roofs, tents, etc. Wearable solar cells could be designed to perform not only in sunlight but also in indoor light.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.