Comparing the planar and porous Nb-doped TiO2 photoanode of triple cation perovskite solar cells

Abstract

Achieving an optimal electron transport layer is an essential step toward fabricating perovskite solar cells with higher power conversion efficiency (PCE). Photoanode and perovskite absorber are among the most influential components which affect the charge generation and transport rates. Here, we report on the photoanode modification and its influence on the triple cation perovskite solar cells. We successfully synthesized and systematically characterized the niobium (Nb) doping into the planar and mesoporous TiO2 electron transport layer. X-ray diffraction patterns, energy-dispersive X-ray spectroscopy maps, together with the optoelectronic measurements, prove higher Nb incorporation efficiency into the planar TiO2 photoanode. Electrochemical impedance spectroscopy, photocurrent density-voltage (J-V), and photoluminescence spectroscopy (PL) confirm that the charge transfer resistance of the photoanodes, transparency, and their dopant density have a considerable influence on the photocurrent generation and collection rates of the PSCs. Owing to the more visible light transmittance, greater charge transfer conductivity, and higher Nb incorporation efficiency, the planar photoanode demonstrates superior performance compared to the mesoporous counterpart. Moreover, J-V results exhibit substantial PCE improvement of 28.8 and 33.1% by the addition of 5 at.% Nb into the mesoporous and planar photoanodes, respectively, compared to the bare TiO2 photoanode. The radiative recombination rate within the perovskite absorber layer drops by Nb incorporation into the TiO2 photoanode, validated by the PL spectra. Remarkably, this radiative recombination quenches more in the planar photoanode, which is due to the lower charge transfer resistance of the planar TiO2 photoanodes.