Photodetectors (PDs), especially those that respond in the infrared region, are highly desirable and have a wide range of applications ranging from cell phones, cameras, and home electronics to airplanes and satellites. Herein, we designed and fabricated PDs based on air-stable α-CsPbI3 QDs and an up-conversion material (NaYF4:Yb,Er QDs) using a facial low temperature spin-coating method. When the α-CsPbI3 QDs are surface-modified using NaYF4:Yb,Er QDs, their optical response is extended to the NIR region to allow broadband application from the UV to visible to NIR region (260 nm-1100 nm). The optoelectronic properties and compositional stability of the devices were also studied in detail. From the results, the PDs are capable of broad-bandwidth photodetection from the deep UV to NIR region (260 nm-1100 nm) with good photoresponsivity (R, 1.5 A W-1), high on/off ratio (up to 104) and very short rise/decay time (less than 5 ms/5 ms). It was found that the photoresponsivity performance of the PDs in this work is better than that of all the other previously reported perovskite QD-based PDs with a lateral device structure. Furthermore, the device performance shows very little degradation over the course of 60 days of storage under ambient conditions. The combination of remarkable stability, high performance broad-bandwidth photodetection, and easy fabrication suggest that these QDs are a very promising semiconducting candidate for optoelectronic applications.