A high-performance and broadband heterojunction photodetector has been successfully fabricated. The heterostructure device is based on a uniform and pinhole-free perovskite film constructed on top of a single-crystal germanium layer. The perovskite/germanium photodetector shows enhanced performance and a broad spectrum compared with the single-material-based device. The photon response properties are characterized in detail from the visible to near-infrared spectrum. At an optical fibre communication wavelength of 1550 nm, the heterojunction device exhibits the highest responsivity of 1.4 A/W. The performance is promoted because of an antireflection perovskite coating, the thickness of which is optimized to 150 nm at the telecommunication band. At a visible light wavelength of 680 nm, the device shows outstanding responsivity and detectivity of 228 A/W and 1.6 × 1010 Jones, respectively. These excellent properties arise from the photoconductive gain boost in the heterostructure device. The presented heterojunction photodetector provides a competitive approach for wide-spectrum photodetection from visible to optical communication areas. Based on the distinguished capacity of light detection and harvesting from the visible to near-infrared spectrum, the designed germanium/perovskite heterostructure configuration is believed to provide new building blocks for novel optoelectronic devices.

Controllable synthesis of tin-doped all-inorganic perovskite (e.g. CsPb1-XSnXBr3) nanocrystals while maintaining tin at the divalent state is of great importance for tuning their optoelectronic properties by changing the chemical composition and geometrical size; however, this remains a non-negligible challenge. In contrast to the conventional high-temperature (>150 °C) synthesis reaction that would more likely facilitate oxidation of divalent Sn2+ to quadrivalent Sn4+, this work demonstrates a facile low-temperature (105-150 °C) hot-injection method to synthesize quantum-confined Sn2+-doped CsPb1-XSnXBr3 nanocrystals with sizes ranging from ∼6.2 nm to ∼8.3 nm depending on the reaction temperature. The optimized reaction temperature of 135 °C led to a Sn2+-doping ratio of 3.4% in CsPb1-XSnXBr3 nanocrystals which exhibited uniform nanoplatelets with an average lateral size of ∼7.4 nm. Furthermore, for the first time, we show that the perovskite nanocrystals are promising for the development of low-cost and trap-assisted photomultiplication UV-photodetectors, and the photodetectors based on CsPb0.966Sn0.034Br3 nanocrystals exhibited wavelength-dependent detectivities in the magnitude of 1011 Jones for UV light extending from 310 nm to 400 nm at a reverse bias of -7 V. The high EQE of ∼1940% at around 340 nm indicates that the devices had a gain at the large reverse bias condition, which is attributed to the formation of interfacial traps by CsPb0.966Sn0.034Br3 nanocrystals that can make the electron injection barrier thin enough to allow electron tunneling in the photodetectors for photomultiplication.