Lead halide perovskites (LHPs) have emerged as promising semiconductors for next-generation optoelectronic devices such as photodetectors (PDs), solar cells, and radiation detectors. LPHs in single crystals (SCs) showed much better stability and optoelectronic properties than the polycrystalline thin-film counterparts due to the absence of grain boundary, lower surface defects, and lower ion migration. Among next-generation LHP SCs, Methylammonium lead bromide (MAPbBr₃) has become the centre of research for the last five years due to its feasible crystal growth and stability under ambient conditions.[1,2] Nowadays, self-powered photodetectors (SPPDs) are paramount in various applications because they can operate in remote locations without any external power sources. Photodiodes are one such device that can be use as SPPDs. MAPbBr₃ SCs-based photodiodes can be formed by doping various metal ions into the host perovskite structure.

In this work, a planar SPPD was developed from metal-doped p-type MAPbBr₃ / n-type MAPbBr₃. At first, separately synthesised p-type Ag⁺ doped MAPbBr₃ and n-type Sb³⁺ doped MAPbBr₃ and optimised their doping concentration for better photovoltaic performance. The planar PD with p-type 0.1% Ag⁺ doped shows favourable photodetection properties, such as responsivity (R) of 3.95 A W-1 and external quantum efficiency of 1093%, almost 20% better than the undoped.[3] Similarly, n-type 0.1% Sb³⁺ doped PD exhibits improved optoelectronic properties because of the combined effect of high electron concentration and low Schottky barrier height (SBH) between the Ag metal electrode and SC. Based on these results, ultimately, a p-n junction photodiode was developed by growing 0.1% Ag⁺ doped MAPbBr₃ SC epitaxially on the facet of 0.1% Sb³⁺ doped MAPbBr₃ SC. Finally, SPPD was fabricated using MAPbBr₃ SC photodiode by depositing asymmetric electrodes to use the combined effect of the built-in electric field in the p-n junction depletion region and the electric field formed by the asymmetric Schottky barrier height to maximise the performance. This p-n junction device incorporated with asymmetric electrodes (Ag and Pt) shows typical photovoltaic behaviour with an excellent open circuit voltage of 0.95 V. This device shows great sensitivity towards the 530 nm illumination without any external bias. Under the mentioned conditions, our device shows responsivity up to 0.41 A W^-1 and a specific detectivity of 6.39 × 10¹¹ Jones. These values are the highest reported for any MAPbBr₃-based SPPDs. Additionally, this device retained 80% performance after 12 hours of continuous illumination at ambient conditions and restored 94% of initial performance after 36 hours of storage under the dark, dry box. This work on p-n junction photodiode can pave the way for designing new potential perovskite-based SPPDs.