The last eight years (2009-2017) have seen an explosive growth of interest in organic-inorganic halide perovskites in the research communities of photovoltaics and light-emitting diodes. In addition, recent advancements have demonstrated that this type of perovskite has a great potential in the technology of light-signal detection with a comparable performance to commercially available crystalline Si and III-V photodetectors. The contemporary growth of state-of-the-art multifunctional perovskites in the field of light-signal detection has benefited from its outstanding intrinsic optoelectronic properties, including photoinduced polarization, high drift mobilities, and effective charge collection, which are excellent for this application. Photoactive perovskite semiconductors combine effective light absorption, allowing detection of a wide range of electromagnetic waves from ultraviolet and visible, to the near-infrared region, with low-cost solution processability and good photon yield. This class of semiconductor might empower breakthrough photodetector technology in the field of imaging, optical communications, and biomedical sensing. Therefore, here, the focus is specifically on the critical understanding of materials synthesis, design, and engineering for the next-stage development of perovskite photodetectors and highlighting the current challenges in the field, which need to be further studied in the future.

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high photoexcitation intensity can lead to room-temperature magneto-photoluminescence and magneto-photocurrent with negative and positive signs, respectively, below the fi eld of 200 mT. Our results provide evidence that the charge recombination and dissociation are spin dependent at room temperature in OMHPs. Essentially, our results indicate that applying a magnetic fi eld can suppress the spin mixing between antiparallel and parallel spin states in electron-hole pairs and consequently decreases the antiparallel spin states but increases the parallel spin states. The change between different spin states in electron-hole pairs can eventually modify the exciton formation when the electron-hole pairs relax into excitons. Because of Pauli Exclusion Principle applied onto excitonic states, the singlet and triplet excitons can have high and low annihilation rates. As a result, decreasing the antiparallel spin states in electron-hole pairs by suppressing the spin mixing can weaken the singlet exciton formation, consequently leading to a decrease on photoluminescence toward the development of negative magneto-photoluminescence. On the contrary, decreasing the exciton formation can slow down the consumption on the electron-hole pairs. This can lead to more electron-hole pairs ready for charge dissociation to generate a photocurrent, generating a positive magneto-photocurrent. Clearly, the spin polarizations can be used as a new approach to control the charge recombination and dissociation in OMHPs. Furthermore, by using the observed magneto-photoluminescence and magneto-photocurrent, we investigate the dissociation effects in electron-hole pair states at different excitation intensities to further understand charge recombination and dissociation at different densities at device-operating condition. We fi nd that the critical bias required to completely quench the magneto-photocurrent and magneto-photoluminescence signals is increased with increasing photoexcitation intensity in OMHPs. This implies that, as the charge density increases with increasing the photoexcitation intensity, the formation of electron-hole pairs is enhanced, requiring a stronger fi eld to complete the charge dissociation toward generating photocurrent. Simultaneously, the line-shape on magneto-photocurrent and magnetophotoluminescence shows a narrowing phenomenon with increasing photoexcitation intensity. This indicates that the electron-hole pairs experience mutual inter-pair interactions and consequently changes the internal interactions within each electron-hole pairs. Clearly, our magneto-optical studies can provide critical understanding on controlling spin-dependent charge recombination and dissociation toward improving the photovoltaic actions in perovskite solar cells. Figure 1 a shows the magneto-photocurrents at different excitation intensities from the continuous wave (CW) laser beam of 532 nm in OMHP solar cells with the device architecture of ITO/PEDOT:PSS/CH 3 NH 3 PbI 3x Cl x /PC 71 BM/TiO x /Al. We Organometal halide perovskites (OM...