While the rate of improvement for organic lead halide perovskite solar cells is slowing, there has been a dramatic increase in cell efficiencies and in the number of cell demonstrations for inorganic cesium lead halide perovskite (e.g., CsPbIXBr3-X) solar cells in the last 2 years. The higher band gap and thermal stability of CsPbIXBr3-X are desirable for tandem solar cell applications and other optoelectronic devices. It is apparent that these cells are performing well optically, with some reaching 90% of their theoretical current output limits. However, low carrier lifetime and high surface recombination limit the voltages and fill factors of these cells, limiting their performance to only 60% of their theoretical efficiency limits. Appropriate transport layer designs (producing positive band offsets), reducing surface recombination velocities (to 103 cm/s), and improving lifetimes (10 μs) are effective strategies for improving efficiencies, allowing cells with thick absorbers to be fabricated, and achieving efficiencies above 80% of their theoretical limits.