Tuneable and spectrally selective broadband reflector – Modulated photonic crystals and its application in solar cells

Cross sectional Scanning Electron Microscopy image of a modulated photonic crystal based amorphous silicon solar cell showing the different layers in the device. The graph shows the angle dependent I-V characteristic of the amorphous silicon solar cell with modulated photonic crystal. [Display omitted] •One dimensional photonic crystal with selectively tunable stopband.•Broad stopband 580–1200 nm dielectric mirror with an integrated reflectance of 97.6%.•Analysis on reflectance tunabilityof photonic crystal by simulation and experiment.•Integration of PC back reflectorin thin film a-Si solar cell replacing metal layer.•Angle dependent study of photonic crystal back reflector applied in a solar cell.•PC reflectors for light trapping and as passivating layer for thin c-Si solar cells. One dimensional photonic crystal has been developed as a broadband dielectric reflector, the stopband of which could be selectively tuned based on absorption spectrum of the absorber material. The design parameters and factors which contribute to the tunability of the photonic crystals are analyzed through simulations and experiments. The photonic crystal structures are fabricated using silicon rich silicon nitride and silicon oxynitride thin films deposited by PECVD at 200 °C. Modulated photonic crystal with a broad bandwidth, having an integrated reflectance of 97.6% in the wavelength range 580–1200 nm has been fabricated and applied in an amorphous silicon thin film solar cell as the back reflector. The optical performance of solar cells with these back reflectors has been studied in the longer wavelength as against the conventional metallic back reflector. The characterization of the thin film silicon solar cell with these photonic structures presented a short circuit current density of 14.77 mA/cm2. The angle dependent behaviour of the photonic crystal has been studied using angle dependent current-voltage measurement and a future prospectus of these structures as passivation layer for ultra thin crystalline silicon solar cells is also highlighted.