The command unzip has its own option unzip -Z1 zipfile.zip to show the actual compressed filename within zipped file which is taking zipinfo's option -1 as it's zipinfo -1 zipfile.zip. so you could simply do as below and there is no need to create a temp directory and mv will done in place in current directory.
for z in *.zip; do unzip "$z"; mv "$(unzip -Z1 $z)""${z%%.*}.txt";done