Ionic Liquids Modulating CsPbI₃ Colloidal Quantum Dots Enable Improved Mobility for High-Performance Solar Cells

Abstract

Colloidal all-inorganic CsPbI 3 perovskite quantum dots (PQDs) have shown tremendous potential in photovoltaic applications in recent years due to their outstanding optoelectronic properties that general metal halide perovskites offer, along with the added advantages that originates from size reduction and the quantum confinement effect. However, the issue of low carrier mobility in PQD films caused by insulating organic ligands capped on the PQD surface still remains to be addressed while aiming for high-efficiency PQD solar cells. Herein, we propose a novel strategy that takes benefits of ionic liquids, which can offer the high polarity and the electron donating ability to boost the mobility of PQD films in photovoltaic devices. Specifically, 1-propyl-3-methylimidazolium iodide to modulate the colloidal CsPbI 3 PQD surface and couple QDs is demonstrated for the first time. The lone pair electrons on the nitrogen of the imidazole ring within the ionic liquid binds to the empty nonbonding surface orbitals of CsPbI 3 PQDs while the long-chain insulating ligands are replaced, which enables not only efficient charge transport but also reduced defect density in the assembled PQD solid films. The resulting CsPbI 3 PQD solar cell shows a significant increase in efficiency with suppressed hysteresis, indicating the impressive potential of this strategy for developing highly efficient PQD solar cells.

Selection, Preparation and Application of Quantum Dots in Perovskite Solar Cells

“…Perovskite quantum dots (PQDs) have been fabricated by researchers as light-absorbing layers due to their high photoluminescence quantum yield (PLQY) and tunable forbidden bands, which are beneficial for enhancing the light capture capability of the devices. Table 6 lists the details of the devices [ 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 ].…”

“…The measurements revealed enhanced electronic coupling and improved hydrophobicity, with the final device achieving a 14.1% PCE. In 2022, Han et al [ 144 ] used 1-propyl-3-methylimidazolium iodide ((Pmim)I) ionic liquid to replace the OA and OAm long-chain insulating ligands on the surface of QDs. The charge transfer rate of the film was increased (the mechanism is shown in Figure 10 d).…”

“…( d ) Mechanistic diagram of ligand action. Reproduced from [ 144 ], with permission from the American Chemical Society, 2022. ( e ) Progress of QD solar cells.…”

How the ionic liquid BMIMBF4 influences the formation and optoelectronic properties of MAPbI3 thin films

“…For this bifunctional passivation approach of MHPs, ionic liquids (IL) have turned out to be especially suitable. 10,[22][23][24][25] For example, Snaith et al mixed 1-butyl-3-methylimidazoliumtetrauoroborate (BMIMBF 4 ) into the precursor solutions of different halide perovskites, which lead to an extraordinary high stability of resulting solar cells and improved optoelectronic lm properties. 26 Another important aspect affecting the optoelectronic properties of perovskites is their morphology, which in turn is decisively determined by the exact crystallization processes that occur during the solution based thin lm preparation.…”

“…For this bifunctional passivation approach of MHPs, ionic liquids (IL) have turned out to be especially suitable. 10,22–25 For example, Snaith et al mixed 1-butyl-3-methylimidazoliumtetrafluoroborate (BMIMBF 4 ) into the precursor solutions of different halide perovskites, which lead to an extraordinary high stability of resulting solar cells and improved optoelectronic film properties. 26…”