METHYLAMMONIUM-LEAD-IODIDE AS INORGANIC CAPPING LIGAND FOR LEAD SULFIDE QUANTUM DOTS AND ITS APPLICATION IN FIELD EFFECT TRANSISTORS

• Main Author: Rizkia, Nisrina
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/34105
• Institution: Institut Teknologi Bandung

Semiconducting quantum dots (QDs) have emerged as a new class of promising materials for electronic, optoelectronic and thermoelectric applications due to their unique size-dependent properties. Their colloidal nature makes them ideal in solution-processed films fabrication resulting in high charge carrier mobility. Methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3, where MA = CH3NH3+ ) has been broadly studied as photoabsorber material, and recently it was shown to be an excellent inorganic capping ligands for lead sulfide quantum dots (PbS QDs). MAPbI3 is used to replace the organic ligands from surface of PbS QDs resulting in lead triiodide anion (PbI3-) terminated QDs that are stabilized in polar solvents, such as propylene carbonate (PC). MAPbI3 capping is able to retain the highly efficient near-infrared photoluminescence of PbS QDs. Moreover, these short inorganic ligands are expected to provide good electronic transport between QDs. However, the use of MAPbI3-PbS QDs for devices has not been shown. In this work, we investigated MAPbI3 for solution phase ligand exchange of PbS QDs and its application in field effect transistors (FETs). The colloidal solution of PbS QDs in hexane undergoes phase transfer from nonpolar to polar phase upon exposure to 1:1 solution of MAI and PbI2 in N- methylformamide. Fourier transform infrared (FTIR) spectra show complete phase transfer of PbS QDs. The quality of the QDs was also monitored with steady state and time-resolved photoluminescence measurements. The steady state photoluminescence of MAPbI3-capped PbS QDs in solution and film are red shifted compared to oleic acid-PbS QDs, showing loosened confinement. The time-resolved photoluminescence show similar lifetimes between oleic acid- capped PbS QDs and MAPbI3-capped PbS QDs in solution, proving the good passivation of the surfaces. Finally, we fabricated MAPbI3-capped PbS QDs transistors using one step deposition on a scalable method. The resulting devices show n-type characteristics with electron mobility up to 5x10-5 cm2V-1S-1. Washing the device with acetonitrile in order to remove the excess ligands results in ambipolar characteristic with electron mobility and hole mobility of 2.9x10-4 cm2V-1S-1 and 2.6x10-7cm2V-1S-1, respectively, with on/off ratio of 1x104 and the appearance of saturation regime in the output curves. This work demonstrates that MAPbI3 is indeed as a promising ligand to improve stability of PbS QDs and can open wider applications of the next generation photovoltaic and optoelectronic devices.