Lead-free halide perovskite photodetectors spanning from near-infrared to X-ray range: a review

Photodetectors based on semiconducting materials are vital building blocks for modern systems containing optoelectronic modules. Although commercial semiconductors have established good performances, they are plagued by complex processing procedures and stalled performances. Recently, lead halide perovskites with superior semiconducting attributes have achieved stunning progress in optoelectronics including photodetectors. However, the toxicity of lead and the ill stability significantly handicap their practical use. Great efforts thus have been devoted to developing lead-free alternatives with improved stability and uncompromised traits. In this review, we thoroughly summarize recent progress in photodetectors based on lead-free halide perovskite variants. The substitution of lead with new elements usually induces a change in structure and ensuingly optoelectronic particularities, which afford unique suitability for a collection of functionality-specified photodetectors. Especially, the family of lead-free variants witnesses a range of bandgaps that construct a broadband photon detection spanning from near-infrared (NIR) to visible regimes. Besides, stress is laid on the X-ray detection capability based on especially bismuth-type lead-free perovskites, of which the strong X-ray absorption, large bulk resistance, suppressed ion migration, and efficient charge collection enable superior X-ray sensitivities and ultralow detection limits. Finally, the challenges and visions are discussed.