Home-building was more labor-intensive then because of cruder tools and equipment, materials were harder to come by and houses were smaller because they didn't include bathrooms or kitchens.
In 1994, North Korea agreed to stop making plutonium, in return for which America and its allies would supply the country with fuel oil and build two Western-designed light-water nuclear reactors (since it is a bit harder to produce weapons-grade materials from such reactors than from the ones North Korea had been building).
Depositing the CIGS materials evenly on glass or metal foil is a lot harder than it sounds, and figuring out a way to mass produce thin films is another big challenge.