Solution-processed near-infrared Cu(In,Ga)(S,Se)2 photodetectors with enhanced chalcopyrite crystallization and bandgap grading structure via potassium incorporation

Joo-Hyun Kim,Jung Ah Lim,Jongtae Ahn,Byoung Koun Min,Tae Joo Shin,Min Kyu Kim,Hyemi Han,Do Kyung Hwang

doi:10.1038/s41598-021-87359-9

Abstract

Although solution-processed Cu(In,Ga)(S,Se)2 (CIGS) absorber layers can potentially enable the low-cost and large-area production of highly stable electronic devices, they have rarely been applied in photodetector applications. In this work, we present a near-infrared photodetector functioning at 980 nm based on solution-processed CIGS with a potassium-induced bandgap grading structure and chalcopyrite grain growth. The incorporation of potassium in the CIGS film promotes Se uptake in the bulk of the film during the chalcogenization process, resulting in a bandgap grading structure with a wide space charge region that allows improved light absorption in the near-infrared region and charge carrier separation. Also, increasing the Se penetration in the potassium-incorporated CIGS film leads to the enhancement of chalcopyrite crystalline grain growth, increasing charge carrier mobility. Under the reverse bias condition, associated with hole tunneling from the ZnO interlayer, the increasing carrier mobility of potassium-incorporated CIGS photodetector improved photosensitivity and particularly external quantum efficiency more than 100% at low light intensity. The responsivity and detectivity of the potassium-incorporated CIGS photodetector reach 1.87 A W−1 and 6.45 times 1010 Jones, respectively, and the − 3 dB bandwidth of the device extends to 10.5 kHz under 980 nm near-infrared light.

Highlights

Photodetectors, which convert optical into electrical signals, play a key role in current information technology[1,2,3]
A six-layered CIG oxide (CIGOx) film was fabricated by applying the precursor coating six times and the K-layer was applied on the third CIG oxide layer, followed by post-chalcogenization comprising selenization and sulfurization
The atomic concentrations of Cu, Na, and K and In, Ga, S, and Se were obtained by atomic absorption spectroscopy (AAS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements, respectively

Summary

Introduction

Photodetectors, which convert optical into electrical signals, play a key role in current information technology[1,2,3]. To further extend the light absorption range to the NIR region, a unique potassium (K)incorporation in the bulk CIGS films is introduced to form a bandgap grading structure with a wide Eg,min region by promoting Se penetration. This wide Eg,min region results in a wide width of space charge region (WSCR) where the charge collection efficiency approaches 1. We demonstrate that the fabricated K-incorporated CIGS photodetectors based on this process exhibit improved photoresponse characteristics with a high sensitivity of R = 1.87 A W−1, detectivity of D* = 6.45 × 1010 Jones, and fast response rate of 0.02 s, which are obtained at far NIR 980 nm and comparable to the performances from other CIGS photodetectors[6,22]. We suggest that the K-incorporated CIGS films have great potential for NIR photodetection applications

Methods

Results

Conclusion