The design can be changed; but this design is as it is in large part because of how much surface area it needs to collect enough sunlight to sustain even its distinctly frugal operation.
Improvements are likely, with better solar panels, better batteries, or both; but you don't beat the fact that optimal insolation is 1366w/m^2; and real world values typically lower, at least on average. A liter of Jet A is 35.3 MJ, so ~9880watt/h. Even at peak insolation, a square meter of solar collection takes a little over 7 hours to amount to as much energy as a liter of jet fuel. Jet engines are, of course, hardly perfectly efficient; but you get some sense of perspective from the fact that a relatively modern design, aimed at fuel efficient operation, like the 787 still has storage for in excess of 100,000 liters of fuel, a big 747-400 more like twice that.
On the plus side, your sunlight supply doesn't weigh anything, or require any volume(though your batteries do, and barring major improvements their energy density is dreadful compared to hydrocarbons); but even given perfectly efficient solar hardware, there just isn't that much energy to work with, by the standards of hydrocarbon aircraft. Any possible design is going to reflect this through some combination of gigantic wing area per unit capacity and a flight plan that sticks relatively carefully to maximally efficient speeds.