If you thought the upper limit of solar cell efficiency was 32 percent in April, think again in May. Last week, MIT News reported on a research team that demonstrated how a silicon solar cell could top the theoretical limit of 32 percent. See you later, Shockley-Queisser Limit, and don’t let the door hit you on the way out. To be clear, William Shockley and Hans J. Queisser can rest easy. The demonstration involved a…