Engineering Band‐Type Alignment in CsPbBr3 Perovskite‐Based Artificial Multiple Quantum Wells

Semiconductor heterostructures of multiple quantum wells (MQWs) have major applications in optoelectronics. However, for halide perovskites—the leading class of emerging semiconductors—building a variety of bandgap alignments (i.e., band‐types) in MQWs is not yet realized owing to the limitations of the current set of used barrier materials. Here, artificial perovskite‐based MQWs using 2,2′,2″‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole), tris‐(8‐hydroxyquinoline)aluminum, and 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline as quantum barrier materials are introduced. The structures of three different five‐stacked perovskite‐based MQWs each exhibiting a different band offset with CsPbBr3 in the conduction and valence bands, resulting in a variety of MQW band alignments, i.e., type‐I or type‐II structures, are shown. Transient absorption spectroscopy reveals the disparity in charge carrier dynamics between type‐I and type‐II MQWs. Photodiodes of each type of perovskite artificial MQWs show entirely different carrier behaviors and photoresponse characteristics. Compared with bulk perovskite devices, type‐II MQW photodiodes demonstrate a more than tenfold increase in the rectification ratio. The findings open new opportunities for producing halide‐perovskite‐based quantum devices by bandgap engineering using simple quantum barrier considerations. Engineering band‐type alignment in CsPbBr3 multiple quantum wells (MQWs) is demonstrated by adapting various organic molecular spacers as quantum barriers. Three different MQWs exhibit a different band offset with CsPbBr3, resulting in a variety of MQW band alignments, e.g., type‐I or type‐II structures. Photodetectors using these MQWs display distinct carrier dynamics and device characteristics that vary distinctly the barrier material.