The effect of superlattice buffer of microcrystalline silicon solar cells

In order to improve the open circuit voltage (V/sub oc/) of /spl mu/c-Si:H solar cells, a p/i buffer layer has been studied using a-Si//spl mu/c-Si superlattice structure. Substrate type solar cells were prepared at 140/spl deg/C onto flat substrate with i-layer thickness of 1/spl mu/m. Two kinds of the buffer layer were examined; one is a-Si single layer with a thickness of 2 to 12nm and the other is a-Si//spl mu/c-Si multilayers. By inserting a single 2nm thick a-Si layer, V/sub oc/ increases from 0.472 V to 0.530V and fill factor (FF) increases from 70.5% to 74.3%. Although the short wavelength response decreases slightly, efficiency increases from 6.1% to 6.4%. Furthermore, we examined a-Si//spl mu/c-Si superlattice structure at pi interface and demonstrate /spl mu/c-Si solar cell with FF of 75.3%. These are attributed to reduction of the diode saturation current by the insertion of wide band gap material, which acts as a barrier.