CsPbBr3 Nanocrystal Induced Bilateral Interface Modification for Efficient Planar Perovskite Solar Cells

Abstract

Organic-inorganic halide perovskite solar cells (PSCs) have drawn tremendous attention owing to their remarkable photovoltaic performance and simple preparation process. However, conventional wet-chemical synthesis methods inevitably create defects both in the bulk and at the interfaces of perovskites, leading to recombination of charge carriers and reduced stability. Herein, a bilateral interface modification to perovskites by doping room-temperature synthesized CsPbBr₃ nanocrystals (CN) is reported. The ultrafast transient absorption measurement reveals that CN effectively suppresses the defect at the SnO₂ /perovskite interface and boosts the interfacial electron transport. Meanwhile, the in situ Kelvin probe force microscopy and contact potential difference characterizations verify that the CN within the upper part of the perovskites enhances the built-in electric field, facilitating oriented migration of the carriers within the perovskite. Combining the superiorities of CN modifiers on both sides, the bilaterally modified CH₃ NH₃ PbI₃ -based planar PSCs exhibit optimal power conversion efficiency exceeding 20% and improved device stability.

Keywords: CsPbBr3 nanocrystals; built-in electric field; defect passivation; gradational incorporation; interface modification.

Figure 1

a) Schematic for CN induced bottom modification of perovskite film. b) The contact angles of water droplets on FTO and SnO₂ without and with different times of CN modification. Steady‐state PL spectra of perovskite films deposited on CN modified SnO₂ ETLs illuminated from c) the FTO‐glass side and d) perovskite film side. e,f) The pseudocolor plots, g,h) transient TA spectra of FTO/SnO₂/PSK and FTO/SnO₂/CN/PSK excited at 400 nm, and i) corresponding normalized decay kinetic curves at 759 nm. Schematics for electron generation and extraction at the interface j) between SnO₂ and PSK or k) between SnO₂ and CN/PSK.

Figure 2

a) Schematic for CN induced top modification of perovskite film. b) Schematic of glancing‐angle XRD test. c) Glancing‐angle XRD patterns of perovskite film with CN top modification in different glancing angles. d) XRD patterns of perovskite films with different concentrations of CN top modification.

Figure 3

a,b) AFM images of PSK and PSK(10%CN). In situ KPFM images of PSK and PSK(10%CN) under c,d) dark condition and e,f) 420 nm light illumination. g,h) Surface potential distributions of PSK and PSK(10%CN) under dark condition and 420 nm light illumination.

Figure 4

a) In situ CPD detection of PSK, CN, and PSK (10% CN) under dark condition and 461 nm light illumination. b) Schematic for the Fermi level of PSK, CN, and PSK(10%CN) under dark condition and 461 nm light illumination. c) Schematic for the changes of Fermi level at the interfaces of PSK/ETL and PSK/HTL.

Figure 5

a) Schematic for CN bilateral interface modification of perovskite film. Characterizations of PSK and 4‐CN/PSK(10%CN) based planar PSCs: b) J–V curves under simulated AM 1.5 illumination; c) steady‐state photocurrent and PCE measured at the maximum power point; d) plots of photocurrent density (J _ph) with regard to the effective bias (V _eff); e) normalized photocurrent (J _ph/J _sat) with regard to V _eff; f) EIS plots tested under dark condition. g) J–V curves of the electron‐only devices based on PSK and 4‐CN/PSK(10%CN) active layer.