2, Seoul National University, Seoul, , Korea (the Republic of)
3, Seoul National University, Seoul, , Korea (the Republic of)
Metal halide perovskites (MHPs) have been studied as active layers in solar cells (SCs) because of its superior optical and electrical properties such as large absorption coefficient ( 5×103 cm-1 ~ 5×104 cm-1 for CH3NH3PbI3) and low exciton binding energy (37–75 meV for CH3NH3PbBr3 and 29–50 meV for CH3NH3PbI3). However, MHP polycrystalline (PC) bulk film based SCs suffered poor reproducibility because surface morphology of MHP PC films were severely affected by the environmental conditions during film formation process such as temperature, atmosphere and surface energy of under-layer.
Here, we report ligand-engineered MHP nanoparticles (NPs) and MHP NP SCs based on uniform MHP NP films. Ligand-engineered MHP NPs which had short organic ligands increased the charge extraction/transfer characteristics in MHP NP films and short-circuit current in MHP NP SCs. We also fabricated the uniform CH3NH3PbBr3 NP/CH3NH3PbI3 NP bilayers by using non-wet stamping process and MHP NP SCs based on them. These bilayer NP films can increase the power conversion efficiency (PCE) of MHP NP SCs because different band gaps of CH3NH3PbBr3 ~ 2.2 eV and CH3NH3PbI3 ~ 1.5 eV increases absorption wavelength, short-circuit current and open-circuit voltage. We also confirmed the effects of ligand engineering and bilayers by conducting photoluminescence (PL) and UV-vis absorption measurements. Our works demonstrated here showed the effective ways to increase the PCE in perovskite NP SCs.