Porous silicon as an intermediate layer for heterojunction solar cells on p-type Si crystalline substrates

The study of the influence of ITO deposition process on the defect formation in the interface region of heterojunctions (HJ) is done. The role of intrinsic a-Si:H and as an alternative a thin porous Si buffer layer is analyzed. It is shown that a thin porous Si as a buffer layer in HJ solar cells leads to the improvement of the HJ solar cells efficiency since this layer serves as a protection one of the Si substrate during the ITO deposition process. By DLTS method it is observed that damages created during the deposition of ITO layer can be essentially suppressed by a thin a-Si:H or thin porous Si buffer layers. In case of porous silicon formation by the electrochemical etching the process is “softer” and this thin intermediate layer has similar properties as a-Si:H concerning the hydrogen concentration and the characteristics of Si-H bonds. This conclusion was derived from the Nuclear Reaction Analysis (NRA) and Raman measurements, which are performed on porous-Si/crystalline Si structures. It is concluded that the main role of a thin porous Si layer in a Si based heterojunction structure is the improvement of the interface properties of HJ solar cells due to a protection of the Si substrate during the depositions of a-Si:H and ITO layers.