To fabricate stable neat FAPbI3 perovskite with a pure α‐phase (pure α‐FAPbI3) is important in the field of photovoltaic commercialization because of its better bandgap than its alloying counterpart with cesium (Cs) or methylammonium (MA) cations. In this study, the first vapor deposited pure α‐FAPbI3 thin film solar cell with a power conversion efficiency (PCE) over 20% is achieved by regulating the phase transition process. It is found that under high humidity conditions, a fast phase transition between high‐purity α‐ and δ‐phase FAPbI3 can be realized. Moreover, theoretical calculations interestingly reveal a phase transition shortcut induced by the abnormal volume contraction that is ascribed to the formation of double hydrogen bonds at a certain H2O concentration. Therefore, a high‐humidity post‐treatment strategy is proposed to fabricate α‐FAPbI3 solar cells with a champion PCE of 20.19% (0.1 cm2) and 18.91% (1 cm2), which is currently the highest recorded value in vapor deposited pure α‐FAPbI3 perovskite solar cells. This study helps to redefine the effect of a water molecule on FAPbI3 solar cells. In addition, the demonstrated scaling‐up possibility provides another perspective for fabricating uniform high‐performance pure α‐FAPbI3 perovskite solar cells.

the Sn-Pb-based perovskite photodiodes were spin deposited onto the drain electrode of indium gallium zinc oxide (IGZO) TFTs. [16] The array showed visible to near-infrared imaging ability with a response speed of 52 ms, dark current of 1.04 × 10 −7 A and I photo /I dark of 5.06 × 10 2 . Albert et al. further demonstrated a flexible sensor array of 640 × 480 pixels for biometric fingerprinting. The device showed dark current as low as 9.7 × 10 −7 mA cm −2 and a faster response speed of 2.7 µs. [18] Deumel et al. showed the integration of single crystal MAPbI 3 on TFT for X-ray imaging with a low detection limit of 6.3 nGy air s −1 . [20] These great advances have brought the perovskite photodetector array closer to practical application. However, the difficulty of these methods is the device complexity and combination of the preparation processes of both devices, which require sophisticated micro/nanofabrication. Furthermore, the photodetector in the sensor array suffers a significant performance loss, for example, reduced on/off ratio and LDR, due to the electrical mismatch. [18] A simpler approach is to fabricate a crossbar array with the photodetectors sandwiched between cross electrodes. This crossbar array offers the highest integration density and is widely used in imaging sensors and memristor arrays. [21][22][23][24][25] A pixel in a crossbar array is usually composed of a photodiode or photoconductor type photodetector. In many research, it is imaged using a mask or a light spot with the selected pixel at a high bias voltage, while the unselected pixels are at 0 V or in a floating state. [22,26,27] This offers a contrast between the illuminated and unilluminated pixels. However, the photodiode With the development of perovskite photodetectors, integrating photodetectors into array image sensors is the next target to pursue. The major obstacle to integrating perovskite photodiodes for dynamic imaging is the optoelectrical crosstalk among the pixels. Herein, a perovskite photodiode-blocking diode (PIN-BD) crossbar array with pixel-wise rectifying property by the vapor deposition method is presented. The PIN-BD shows a large rectification ratio of 3.3 × 10 2 under illumination, suppressing electrical crosstalk to as small as 8.0% in the imaging array. The fast response time of 72.8 ns allows real-time image acquisition by over 25 frames per second. The imaging sensor exhibits excellent imaging capability with a large linear dynamic range of 112 dB with 4096 gray levels and weak light sensitivity under 1.2 lux.

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