Now ,when I am printing the repeater it's opening in window and having very small size.
That's because you have asked it to be opened that way.
See this line:
var printscreen = window.open('','','left=1,top=1,width=1,height=1,toolbar=0,scrollbars=0,status=0');
Now the parameters top, left (ie only), width, height decides the position and height and width of the window.
You have specified height and width value as 1. Min value is 100px. So the size of the window will be 100px by 100px.
Change these values according to your requirement and it should be fine.
And this link should also help you -
Window open() Method[
^]
Hope this helps!