Reduced electron relaxation time of perovskite films via g-C3N4 quantum dot doping for high-performance perovskite solar cells

Abstract

Perovskite film-quality is a crucial factor to improve the photovoltaic properties of perovskite solar cells, which is closely related to the morphology of crystallization grain size of the perovskite layer. However, defects and trap sites are inevitably generated on the surface and at the grain boundaries of the perovskite layer. Here, we report a convenient method for preparing dense and uniform perovskite films, employing g-C₃N₄ quantum dots doped into the perovskite layer by regulating proper proportions. This process produces perovskite films with dense microstructures and flat surfaces. As a result, the higher fill factor (0.78) and a power conversion efficiency of 20.02% are obtained by the defect passivation of g-C₃N₄QDs.

Fig. 1. (a) Device architecture (b and c) the contact angle testing and surface-view SEM images of perovskite films without and with the optimized concentration of additive (30). (d) XRD patterns of perovskite films with different doping ratios of g-C₃N₄QDs films deposited on PEDOT:PSS/FTO. The 20/30/40/50 corresponding to the 0.2 wt%/0.4 wt%/0.6 wt%/0.8 wt%, respectively. (e and f) AFM images of perovskite films without and with the optimized concentration of additive (30).

Fig. 2. (a) The absorption spectrum of perovskite films without and with the optimized concentration of additive (30). (b) The steady-state photoluminescence spectrum of perovskite films perovskite films without and with the optimized concentration of additive (30) deposited on the PEDOT:PSS/FTO. (c) The XPS spectra of perovskite films without and with the optimized concentration of additive (30). (d–f) High-resolution XPS C 1s/Br 3d/N 1s spectra of perovskite films without and with the optimized concentration of additive (30).

Fig. 3. (a) TA spectra of perovskite films with different g-C₃N₄QDs doping ratios at 589 fs Normalized kinetic traces after excitation at 460 nm. (b and c) TA spectra of perovskite films without and with the optimized concentration of additive (30) at 1 ps. (d) Liquid-state 1H magnetic resonance (NMR) spectra of (a) perovskite precursor solutions with and without g-C₃N₄QDs (DMF) in deuterated N,N-dimethylformamide-d7 (DMF-d7) and (e) magnification of the scale between 7 and 10 ppm, (f) 2–4 ppm.

Fig. 4. (a) J–V curves of the devices without and with the optimized concentration of additive (30). (b) EQE spectra and their integrated current densities. (c) OCVD curves of the PSCs without and with the optimized concentration of additive (30). (d) Dark current–voltage curves of devices with different doping ratios. (e) Evolution of trap density during devices with different doping ratios. (f) Hole-only devices without and with the optimized concentration of additive (30) with the structure shown in the inset.