シリコン系ナノ結晶表面での多重励起子の生成

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SiSn-ncs were fabricated by laser ablation in liquid media technique that generates high localized plasma on the surface of amorphous SiSn target. This method synthetized SiSn-ncs alloys that was not possible using conventional techniques such as thin film deposition, high frequency plasma enhanced chemical vapor deposition, or pulsed laser deposition. The nanoparticles generated reach a quantum confinement size about 4nm with clear atomic plans observed by transmission electron microscopy. SiSn-ncs were analyzed by synchrotron radiation XRD to estimate a Si0.88Sn0.12-ncs alloys that can correspond theoretically to direct energy gap transition. Optical bandgap was estimated to be 0.81eV by absorbance measurements, which is well below the silicon bandgap. A low concentration of oxygen on the surface of SiSn-ncs was underlined by Fourier transient infrared spectra, which is of great importance for the stability over time of the devices.The photovoltaic properties of SiSn-ncs were also analyzed using hybrid solar cell devices. Our findings underlines an improvement of the short-circuit current for devices using conjugated polymer PTB7 mixed with SiSn-ncs as active layer. This improvement is related to a better absorption at longer wavelengths due to the low energy band gap and also due to its possible direct transition. An improvement of the open-circuit voltage is also confirmed, related to the bulk heterojunction quality. It is the first report about the photovoltaic effect of SiSn-ncs alloy.