Here, the primary focus is on those approaches to solar energy conversion that strive to achieve very high ef ciencies by exploiting
processes that have smaller losses than a diode-based approach including hot-carrier collection, multiple electron–hole pair cre- ation, and thermophotonics where the theoretical maximum ef - ciencies are in excess of the 31% Shockley–Queisser limit for a single-junction device. In this case, the allowed cost of the cell can be higher. An alternative is to develop moderate-ef ciency devices ( 15%) at extremely reduced costs. This is where print- able organic solar cell devices and other approaches that are not capital- or energy-intensive might become important. Achieving the goal of