Red-shifted photoluminescence and gamma irradiation stability of 'micromorph' (nc-Si/SiOx)/DLC down-converter anti-reflection coatings

摘要

Down-converting "micromorph" silicon dioxide films with embedded silicon nanocrystals (nc-Si) covered by diamond-like carbon (DLC) are fabricated. DLC used as a radiation-protective, stabilizing and anti-reflection coating is found to modify optical and structural properties of nc-Si. The films are in detail characterized employing scanning electron microscopies, energy dispersive X-ray, Raman and FTIR spectroscopies. The existence of amorphous and nanocrystals phases in nc-Si/SiOx films has been confirmed using Raman spectroscopy. The impact of gamma-irradiation on the DLC film was also shown. The main benefit is that photoluminescence (PL) spectrum of nc-Si/SiOx after deposition of DLC shifts in the infrared region close to the maximum of Si-based solar cells photoresponse with simultaneous PL enhancement by about 1.2 times. This effect has been explained by the passivation of non-radiative recombination centers in nc-Si/SiOx by H atoms. Studying the influence of gamma-irradiation on the DLC coatings, the decrease of integral PL intensity of the structures due to the radiation damages of C-H-n bonds has been found. Moreover, gamma-irradiation increases the disorder of C-H-n bonds in DLC as well as decreases the optical transmittance by similar to 20% in the range of 500 to 1100 nm, possibly, due to a weak graphitization of the films. The results show that nc-Si films with DLC as an antireflection, protection and down-converting coating might be considered as a perspective combination to improve the efficiency and degradation stability of solar cells.