Plasmonic assisted enhancement of optical absorption within a thin layer of amorphous silicon (a-Si:H) by incorporating a periodic array of spherical metal nanoparticles on the front side of the a-Si:H layer has been demonstrated by solving Maxwell’s curl equations using a finite difference time domain (FDTD) method. For different particle sizes between 40 and 80 nm, the interparticle spacing has been optimized to yield maximum absorption of AM1.5G solar radiation. By increasing the interparticle coupling, a red-shift up to 280 nm is observed in the peak of broadband absorption behavior within a-Si:H layer. Meanwhile, a comparison between spherical Ag, Al and Au nanoparticles of fixed size is made with respect to the optical absorption enhancement within a-Si:H for the wavelength range from 400 to 800 nm from which we can choose the wavelength range over which a particular type of metal nanoparticle will be useful.
In this paper, we have used Finite Difference Time Domain method for numerically calculating the absorption spectra within a thin layer of hydrogenated amorphous silicon (a-Si:H) with the front surface regularly patterned with spherical Ag nano particles. We have considered a wide range of particle radius (40 nm≤R≤200 nm) for including nano particles that have dipole dominated extinction spectra as well as the particles that can support multipole plasmon resonances. On performing the size variation analysis, constant surface coverage values (S) have been maintained so that the shading effect by the nano particles array will remain same for all particle sizes. We demonstrate that, for effective contribution to the absorption within the a-Si:H layer, there exists a clear distinction between the smaller size nanoparticles which support dipolar resonance and the larger size nano particles capable of producing higher order plasmon modes in terms of S values. The larger particles require much greater coverage than that of smaller particles for efficient plasmonic enhancement. These observations can have considerable importance in designing plasmonic solar cells or other optoelectronic devices that involve various sized Ag nano particles to enhance the optical absorption within an absorber layer.
Abstract.We investigate the passivation properties of the hot-wire CVD deposited thin intrinsic a-Si:H layers grown at different substrate temperatures, Tsub, ranging from 150C -250C, on n type <100> crystalline Si (c-Si) substrates. Highest effective minority carrier lifetime of 288 µs at 10 15 cm -3 injection level was obtained on symmetrically passivated c-Si wafers with a-Si:H layers (~ 9 nm ) grown at Tsub = 200C whereas for the greater or lower Tsub , the respective values of eff drop. The cross section TEM results revealed mixed phase epitaxy for Tsub = 250C that apparently indicates its detrimental effect on passivation. The defect densities and Urbach energy values within respective bulk a-Si:H films were also compared which lead us to conclude that there exists a balance between having an electronically superior a-Si:H film and reduced defect densities at the a-Si:H/c-Si interface for effective passivation. Finally, prototype hetero-junction solar cells having structure: ITO (95 nm)/ (p) a-Si:H (10 nm)/ (i) a-Si:H (9 nm)/c-Si (280µm) / (i) a-Si:H (9 nm)/ (n+) Si:H (30 nm)/Al were fabricated. A comparably higher Voc of 0.57 V was found for solar cells grown around Tsub of 175C and the reasons for the same are discussed.
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