Regensburg 2010 – scientific programme

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KR: Fachverband Kristallographie

KR 5: Topical Session Photovoltaic Materials I (with MM and BV MatWerk)

KR 5.4: Talk

Wednesday, March 24, 2010, 11:15–11:30, H4

Optical and structural properties of MBE grown silicon nanodots for photovoltaic application — •Maurizio Roczen, Enno Malguth, Orman Gref, and Manfred Schmidt — Helmholtz-Zentrum Berlin, Berlin, Deutschland

Third generation Solar cells are aimed to exceed the Queisser-Shockley Limit of 30 % efficiency for single junction silicon solar cells by utilizing the quantum size effect (QSE). In theory, the bandgap of nano-sized silicon structures (< 5 nm) widens with decreasing size. A hetero emitter consisting of silicon nanodots embedded in a SiO₂ matrix could therefore serve as an energy selective contact allowing the extraction of high energy carriers before thermalization takes place. The SiO₂ matrix allows passivation of an adjacent c-Si absorber and of the nanodots themselves. To grow crystalline silicon nanostructures of the required size, amorphous silicon nano layers were deposited onto plasma oxidized Si-wafers and silica substrates by e-beam evaporation at ultra high vacuum. Annealing the samples above 620 ^∘C leads to the formation of separate crystalline spheres. Both atomic force and scanning electron microscopy show a clear tendency of decreasing sphere size for thinner primal layers. Crystallinity is confirmed by Raman experiments. To observe the quantum size effect, absorption and photo luminescence measurements were carried out as well as surface photo voltage measurements to check the density of states at the interface. Recent results on doped nanodots are discussed.