Limits to Hole Mobility and Doping in Copper Iodide

Abstract

Over one hundred years have passed since the discovery of the p-type transparent conducting material copper iodide, predating the concept of the “electron–hole” itself. Supercentenarian status notwithstanding, little is understood about the charge transport mechanisms in CuI. Herein, a variety of modeling techniques are used to investigate the charge transport properties of CuI, and limitations to the hole mobility over experimentally achievable carrier concentrations are discussed. Poor dielectric response is responsible for extensive scattering from ionized impurities at degenerately doped carrier concentrations, while phonon scattering is found to dominate at lower carrier concentrations. A phonon-limited hole mobility of 162 cm2 V–1 s–1 is predicted at room temperature. The simulated charge transport properties for CuI are compared to existing experimental data, and the implications for future device performance are discussed. In addition to charge transport calculations, the defect chemistry of CuI is investigated with hybrid functionals, revealing that reasonably localized holes from the copper vacancy are the predominant source of charge carriers. The chalcogens S and Se are investigated as extrinsic dopants, where it is found that despite relatively low defect formation energies, they are unlikely to act as efficient electron acceptors due to the strong localization of holes and subsequent deep transition levels.

Computational prediction and characterization of CuI-based ternary p-type transparent conductors

“…It has been shown in ref. 38 that in g-CuI a constant t = 10 fs yields a room-temperature mobility m comparable to the one obtained from MRTA calculations that treat scattering mechanisms explicitly. We therefore assume this value of t in our transport calculations within CRTA for the ternary CuI-based compounds.…”

“…We note that our MRTA-PBEsol calculations for g-CuI (m h = 44.56 cm 2 V À1 s À1 and m h = 22.85 cm 2 V À1 s À1 for n h = 10 16 cm À3 and n h = 10 20 cm À3 , respectively), as well as CRTA-PBEsol calculations (m h = 25.46 cm 2 V À1 s À1 and m h = 26.68 cm 2 V À1 s À1 for n h = 10 16 cm À3 and n h = 10 20 cm À3 , respectively) are consistent with MRTA-PBE0/PBEsol results in ref. 38 (m h = 41.3 cm 2 V À1 s À1 and m h = 32.6 cm 2 V À1 s À1 for n h = 10 16 cm À3 and n h = 10 20 cm À3 , respectively) at room temperature.…”

“…The first-principles input for all transport calculations was obtained with the PBEsol functional including spin-orbit coupling (as done in ref. 38). For g-CuI the scissor operator, extracted from modified HSE06 calculations, was applied in AMSET to correct the underestimated PBEsol band gap.…”

“…32,[35][36][37] Recently, sulfur and selenium substitutions on the iodine site were identified as the only relatively shallow acceptors for further p-type doping of CuI. 32,38 Both S and Se substitutions were predicted to have low formation energies and lead to higher hole concentrations than Cu vacancies. 32 Moreover, moderate S and Se doping does not modify significantly neither the absorption spectrum of CuI nor the hole effective masses and therefore the improved hole concentration can potentially positively impact conductivity without deteriorating transparency.…”

Enhanced Conversion Efficiency in MAPbI3 Perovskite Solar Cells through Parameters Optimization via SCAPS-1D Simulation

“…CuI has a direct bandgap that is typically reported to be around 3.1 eV, making it transparent to visible light [37]. One of the significant advantages of CuI is its relatively high hole mobility compared to other p-type semiconductors [38]. CuI is chemically stable under a wide range of conditions and can be easily doped with various elements to fine-tune its electrical and optical properties [39].…”