Metal halide perovskite solar cells are rapidly approaching performances that can rival those of crystalline silicon. After only 5 years of intensive research, the record certified perovskite research solar cell efficiency is 22.1%, while the record certified multi-crystalline silicon cells are at 21.9%, which is the dominant commercially deployed PV technology. For the most advanced c-Si concepts, the last efficiency gains are being squeezed out, with efficiencies approaching 27%. Although improvements in perovskite solar cell efficiency can be expected over the next few years, single junction perovskite solar cells will always be limited to performances near or only slightly better than c-Si. Mainstream PV module manufacturing costs have continued to diminished so extensively over the last decade, that now the cost of the module amounts to less than half the overall solar PV installation. Most of the non-module costs, referred to as the balance of systems (BoS), scale with area of deployed PV rather than power generated. Therefore, increasing the overall power output of the module per unit area, i.e. efficiency, is the surest means to continue to drive down the overall cost installed PV generated electricity. Therefore, we need to develop a strategy and road map, which will lead perovskite solar cells to much higher efficiency than c-Si.
Here I will present a combination of both experimental and theoretical work on multi-junction perovskite solar cells. I will demonstrate how efficiencies significantly in excess of 30% will be achievable, and I will present experimental work progressing towards this goal.