Addressing a rally in Iowa, he said the panels would provide cheap energy and help to pay for the controversial wall.
He suggested the plan was his own, saying: "Pretty good imagination, right? Good? My idea."
However, solar panels have been included in designs for the wall submitted by companies.
During his campaign, Mr Trump pledged to build a wall along the Mexican border to stop illegal immigration and drug trafficking.
He insisted he would make Mexico foot the bill, but President Enrique PeÃ±a Nieto has dismissed the idea.
Mr Trump told cheering supporters at a campaign-style rally in Cedar Rapids on Wednesday that he would "give you an idea that nobody has heard about yet".
"We're thinking of something that's unique, we're talking about the southern border, lots of sun, lots of heat. We're thinking about building the wall as a solar wall, so it creates energy and pays for itself. And this way, Mexico will have to pay much less money, and that's good, right?"
He added: "Solar wall, panels, beautiful. I mean actually think of it, the higher it goes the more valuable it is. Pretty good imagination right? Good? My idea."
More than 200 companies are believed to have responded to an invitation from the Department of Homeland Security (DHS) to submit designs for the wall. Among them was one from Gleason Partners in Las Vegas that proposed a wall of steel, cement and solar panels.
The DHS told the BBC that 20 companies had been shortlisted.
In April, US media reported that President Trump had raised the idea with Republican Congressional leaders in talks at the White House.
The idea of a solar panelled wall was also proposed in an article by an environmentalist and an academic last year in the Huffington Post and another article for the Wall Street Journal by two academics in March.
US President Donald Trump has told supporters that his proposed wall along the border with Mexico could have solar panels fixed to it.