Well long-term stability of organic PV materials hasn't really been shown so I wouldn't say it's sustainable. It's certainly technologically feasible. It unlikely to be very economically viable because organic cells are at most half as efficient as silicon, probably a factor 3 worse on module level, and if you factor in the reduced light intensity on facades you quickly reach a stage where the area of organic PV needed on a facade to produce a given output power is over 10 times the area of Si modules needed on the roof. Maybe if you include it while the facade is being assembled it can make sense, but I don't see how it would be financially worthwhile to retrofit an existing facade.