Understanding Transport in Heterojunction Contact Stacks by Simulating Silicon Heterojunction TLM Structures

Most modern silicon heterojunction solar cells use electron/hole-selective contacts in order to efficiently collect photogenerated carriers. Carrier-selective contacts are important as they block minority carriers and optimize the collection of majority carriers. However, these contact stacks contribute to the resistive loss of the solar cell which is detrimental to the overall device performance. In this paper we analyze the origin of these losses in a hole-collecting contact stack which consists of aSi:H(i)/a-Si:H(p)/ITO(n ⁺ )/Ag through experiments and simulations. We analyze how the contact resistivity of the structure varies with changes in the intrinsic amorphous silicon layer thickness, temperature and ITO(n ⁺ ) doping. The transmission line method was used to characterize the resistive losses of the contact stack. The simulations were conducted using a commercial device simulator SILVACO. We include the ITO as a n-type semiconductor layer in our simulations.