  Solution-processed intrinsic ZnO and Al doped ZnO (ZnO:Al) were spin coated
on textured n-type c-Si wafer to replace the phosphorus doped amorphous silicon
as the electron selective transport layer (ESTL) of the Si heterojunction (SHJ)
solar cells. Besides the function of electron selective transportation, the
non-doped ZnO was found to possess certain passivation effect on c-Si wafer.
The SHJ solar cells with different combinations of passivation layer (intrinsic
a-Si:H, SiOx and non-doped ZnO) and electron transport layer (non-doped ZnO and
ZnO:Al ) were fabricated and compared. An efficiency up to 18.46% was achieved
on a SHJ solar cell with an a-Si:H/ZnO:Al double layer back structure. And, the
all solution-processed non-doped ZnO/ZnO:Al combination layer presents fairly
good electron selective transportation property for SHJ solar cell, resulting
in an efficiency of 17.13%. The carrier transport based on energy band diagrams
of the rear side of the solar cells has been discussed related to the
performance of the SHJ solar cells.
