Analysis of thin layers and interfaces in ITO/a-Si:H/c-Si heterojunction solar cell structures by secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) analysis of In, O, Si, and H concentrations versus depth distributions in ITO(In-Sn-O)/(n,p)a-Si:H/(p,n)-Si and ITO/(p)-Si heterojunction (HJ) solar cell structures was performed. SIMS measurements show some peculiarities of the element profiles in the interface of ITO/a-Si:H and a-Si:H/Si regions. These peculiarities can be attributed to the non-homogeneities (In-rich nanostructures, small dents or mounds) of the ITO layer. It is shown that the formation of In-rich nanostructures is more pronounced in case of ITO growth on a (p)a-Si:H/(n) Si substrate at 230 °C. SIMS profiles obtained from such non-homogeneous areas can show a penetration of In into the Si bulk, which is not a real distribution. A hydrogen redistribution from the a-Si:H layer into the neighboring ITO and Si layers in case of ITO/(n,p)a-Si:H/(p,n)-Si structures as well as hydrogen gettering to the ITO/(p)-Si interface was detected. It is concluded that the final heterojunction structure of ITO/(n,p)a-Si:H/(p,n)c-Si is rather complex and includes in addition to the individual ITO, a-Si:H and Si layers also intermediate ones with different composition.