How can i show post_class() within output loop?

You should use get_post_class()

From Codex:

get_post_class() is not simply a non-echoing alternative to
post_class(). get_post_class() does not return a string, but an array
that must be processed to produce text similar to what is echoed by
post_class().

So

$classes = get_post_class();
$output="<div id="" . get_the_ID() . '" class="' . implode(" ", $classes) . '"></div>';