Title: Stability and Electrical Performance Improvement of Transparent p-Type CuI for Large Area Electronics

Abstract

The transparent electronic materials have been essential electronic components in large area electronics, such as display, thin-film solar cell, and wearable electronics. Especially the a-IGZO and ITO have been successfully implemented as thin-film transistor and transparent electrode with excellent electron mobilities over 10 cm²/Vs and high conductivity over 4000 S/cm. Although there have been great success on these n-type materials, the p-type counterparts are still missing for industrial applications. During several decades of intensive research efforts, there have been reports on transparent p-type materials, such as SnO, NiO_x, delafossite, and LnCuOCh. However, insufficient carrier mobiltiy, lack of proper doping methods, and chemical instability are still existing as critical barrier for industrial application of transparent p-type materials for large area electronics.

We have recently developed transparent p-type electronics with CuI for p-type thin-film transistor (TFT) and p-type transparent conducting electrode (TCE). Initially, with the mild processing of CuI thin-film with acetonitrile at room temperature, we achieved successful control of iodine vacancy and decent TFT performance of hole mobility (mh) of 0.44 cm²/Vs and current on/off ratio (I_on/I_off) of 5×10².[1] As a continuous effort, the hole concentration suppression with Zn doping of CuI resulted high performance transparent TFT with m_h of 5.3 ± 0.5 cm²/Vs and high I_on/I_off of 10⁶ - 10⁷.[2] For transparent p-type conducting electrode, the S doping of CuI was achieved with liquid iodination process. The heavily S-doped CuI have been achieved with unique liquid iodination and solution-process.[3,4] Especially, the unprecedent control of iodine concentration and reaction temperature in liquid iodination showed large hole concentration (n_h) of 3.25 × 10²⁰ cm^-3 and high conductivity (s) of 511 S/cm with optical transmittance over 80 % at 550 nm (T₅₅₀).[3,4] Further application of p-doped CuI was demonstrated for thermoelectric applications. Moreover, the solution processing of highly conductive CuI:S was also achieved.[5] With the continuous development of materials and processing methods, the CuI could provide alternative solutions for high performance transparent p-type electronics.

References

[1] A. Liu, H. Zhu, W.-T. Park, S.-J. Kang, Y. Xu*, M.-G. Kim*, Y.-Y. Noh*, Adv. Mater., 30, 1870258 (2018).

[2] A. Liu, H. Zhu, W.-T. Park, M.-G. Kim*, Y.-Y. Noh*, Nat. Commun., 11, 4309 (2020).

[3] K Ahn. G. H. Kim, S.-J. Kim, G.-S. Ryu, P. Lee, B. Ryu, J. Y. Cho, Y.-H. Kim, J. Kang, H. Kim, Y.-Y. Noh*, M.-G. Kim*, Chem Mater. 34, 10517 (2022).

[4] G. H. Kim, H.-B. Kim, H. Kim, J.-H. Cho, J. Ryu, D.-W. Kang, I. Chung, H. Jang*, K. Ahn*, M.-G. Kim*, Small DOI: 10.1002/smll.202403133 (2024).

[5] M. Son, G. H. Kim, O. Song, C.H. Park, S. Kwon, J. Kang, K. Ahn*, M.-G. Kim*, Adv. Sci. 11, 2308188 (2024).