Visualizing carrier transport in hybrid-perovskite based lateral metal-semiconductor-metal structures
N. Ganesh a, A.Z. Ashar a, Sumukh Purohit a, K.L. Narasimhan b, K.S. Narayan a
a Chemistry and Physics of Materials Unit (CPMU), Jawaharlal Nehru Center for Advanced Scientific Research, Jakkuru, Bengaluru, Karnataka 560064, India, Bengaluru, India
b Center for Nano Science and Engineering (CENSE), Indian Institute of Science, Bengaluru, India
Proceedings of SUNRISE September Symposium 2021 ‘Powering Green Recovery’ (SUNRISEIII)
Online, Spain, 2021 September 20th - 22nd
Organizers: Hari Upadhyaya, Adrian Walters, James Durrant, Sara Walters and Georgia Bevan
Invited Speaker, N. Ganesh, presentation 043
Publication date: 14th September 2021

The high performance of hybrid perovskite-based devices is attributed to its excellent bulk-transport properties. However, carrier dynamics at the metal-perovskite interface and its influence on device operation are not widely understood. Here we explore the microscopic origins of the dominant transport mechanisms in methylammonium lead iodide (MAPbI3) perovskite-based asymmetric metal-electrode lateral devices, with inter-electrode length varying from 4 μm to 120 μm. The device operation characteristics exhibit a cross-over of the transport regimes, from the ohmic to the space-charge limited current (SCLC) characteristic as a function of the inter-electrode length and the applied bias. The potential landscape imaged using spatially resolved Kelvin-probe measurements indicates the presence of a transport barrier at the metal-MAPbI3 interface. Additional observation of a finite electric field across the bulk confirms minimal ion-screening effects on the observed transport characteristics. Further, we study the influence of local photo-excitation using near-field scanning photocurrent microscopy. Photocurrent profiles across the device exhibit dominant recombination and charge-separation zones. In the presence of an external bias, the asymmetric photocurrent profile points to the unbalanced nature of carrier transport. These lateral devices exhibit photodetector characteristics with a responsivity of ≈ 54 mA/W in self-powered mode, and ≈ 6.2 A/W at 5 V bias, in short-channel devices (4 μm). Moreover, the low device capacitance enables light-switching transient response of ~12 ns, suitable for high-speed operational applications.

We acknowledge the Department of Science and Technology, Government of India, and EPSRC-UKRI Global Challenge Research Fund project, SUNRISE (EP/P032591/1), for the financial assistance. SP acknowledges DST-INSPIRE for the fellowship.

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