President Donald Trump still wants to build a southern border wall — and he wants to be able to see through it.

In comments made to reporters aboard Air Force One on Wednesday night en route to Paris, Trump outlined the possible design parameters of the divisive barrier he has proposed for the U.S.-Mexico border. Trump maintained that he was "not joking" about putting solar panels on the wall to potentially help cover the cost.

He also contended that any wall would have to be transparent — "you need to be able to see through it."

Here are his comments about the wall, as released by the White House on Thursday:

Question: You were joking about solar, right?

Trump: No, not joking, no. There is a chance that we can do a solar wall. We have major companies looking at that. Look, there's no better place for solar than the Mexico border -- the southern border. And there is a very good chance we can do a solar wall, which would actually look good. But there is a very good chance we could do a solar wall.

One of the things with the wall is you need transparency. You have to be able to see through it. In other words, if you can't see through that wall — so it could be a steel wall with openings, but you have to have openings because you have to see what's on the other side of the wall.

And I'll give you an example. As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don't see them -- they hit you on the head with 60 pounds of stuff? It's over. As cray as that sounds, you need transparency through that wall. But we have some incredible designs.

As a candidate, Trump repeatedly promised not only to build the barrier on the southern border to curb illegal immigration but also to make Mexico pay for it. So far, Mexico has refused to pay for it, while congressional Democrats and some Republicans have pushed back on the White House's request for federal funding to build it.

Construction has not started.