3.2 Contact resistance of a-Si:H(i)/MoOx/ICO/Ag
stack
The contact resistance related to the carrier selection transport layer
has a significant impact on carrier collection efficiency and solar cell
performance. Therefore, investigation of contact resistances of the SCH
solar cells, especially the MoOx HTL side (back side
here), is imperative. The main methods for contact resistance
measurement include the rectangular transmission line method
(TLM)[31], the Cox and Strack method
(CSM)[32], and the extended CSM
(ECSM)[33]. The electrode structure for CSM and
ECSM are the same and it is employed here for contact resistance
measurement as shown in Fig. 3 (a). The a-Si:H(i),
a-Si:H(p+), TCO and Ag electrodes were deposited
successively on the rear side of a p-type silicon wafer to form an ohmic
contact. Front side of the p-type silicon wafer was deposited with
a-Si:H(i), MoOx, TCO, and Ag in sequence with a metal
mask. The purpose of using p-type Si wafer is to reduce the junction
effect.
The I-V curves corresponding to
c-Si(p)/a-Si:H(i)/MoOx/ICO/Ag contacts with different
electrode diameters are plotted in Fig. 3(b). The obvious rectification
characteristic indicates that ohmic contacts are not formed. The CSM
method is not appropriate for the device featuring junction resistance.
Therefore, the ECSM method which can eliminate the impact of
rectification effect is used to analyze the contact resistance of the
c-Si(p)/a-Si:H(i)/MoOx/ICO/Ag stacks.