Should I wait to invest in solar until more efficient solar panels are available?
Medium long answer:
If you think about deferring an investment until you have an optimal purchase, you would never have bought a cellphone, a computer, a car etc.
Your main question is more "When do I want to start saving on your electric bill?"
When googling solar panel breakthroughs, one can easily find plenty of promising research. The problem is that going from a research lab to something that is commercially available, takes a lot of time and large investments. People buying solar panels want it to come from a proven technology, with a minimum of 20 years of warranties and all the international certifications that come with good panels. Below is a graph of all solar efficiency breakthroughs since 1975 on a single chart.
Another important point is that solar panels are not the only part in a solar system. One needs an inverter to convert DC power to AC power, racking to hold the panels onto the building, engineering, permitting and labor to install the system. With the price drop in solar cells over recent years, the best way to determine the right time to go solar for you is just by judging how long you'll be in the home you own now.
The graph from Bloomberg shows the average weekly spot price for polysilicon solar modules.
Conclusion: Delaying an investment in solar solely based on the belief that a major breakthrough that would "double the efficiency" of commercially available solar cells would come, is a risky bet. Efficiencies do increase and prices did drop, but it shouldn't be the only reason for delaying an investment in solar.
Read our full Guide to Go Solar here