Modification of NiOx hole transport layers with 4-bromobenzylphosphonic acid and its influence on the performance of lead halide perovskite solar cells

Abstract

Lead halide perovskites have proved to be exceptionally efficient absorber materials for photovoltaics. Besides improving the properties of the perovskite absorbers, device engineering and the optimization of interfaces will be equally important to further the advancement of this emerging solar cell technology. Herein, we report a successful modification of the interface between the NiO x hole transport layer and the perovskite absorber layer using 4-bromobenzylphosphonic acid based selfassembled monolayers leading to an improved photovoltaic performance. The modification of the NiO x layer is carried out by dip coating which allows sufficient time for the self-assembly. The change in the surface free energy and the non-polar nature of the resulting surface is corroborated by contact angle measurements. X-ray photoelectron spectroscopy confirms the presence of phosphor and bromine on the NiO x surface. Furthermore, the resultant solar cells reveal increased photovoltage. For typical devices without and with modification, the photovoltage improves from 0.978 V to 1.029 V. The champion V OC observed was 1.099 V. The increment in photovoltage leads to improved power conversion efficiencies for the modified cells. The maximum power point tracking measurements of the devices show stable power output of the solar cells.

Applications of Self‐Assembled Monolayers for Perovskite Solar Cells Interface Engineering to Address Efficiency and Stability

“…By using Br-BA, they achieved an impressively high efficiency of 18.4% with enhanced V oc (1.11 eV) and J sc (21.7 mA cm −2 ). Recently, Mangalam et al [135] used 4-bromobenzylphosphonic acid-based SAMs for NiO x p-i-n PSCs, Figure 8d. The V oc increased from 0.978 to 1.029 V, leading to improved device performance and reduced J-V hysteresis.…”

“…They attribute the increased V oc to a deeper valence band energy of NiO after SAM modification. [135] Similarly, Zhang et al [136] utilized ferrocenedicarboxylic acid (FDA) for NiO surface modification, improving the device performance from 15.13% to 18.20%, along with increasing the UV stability and eliminate J-V hysteresis. The FDA modified NiO x based sample retained 49.8% of its original efficiency after exposure to UV light for 24 h as compared to only 3.8% efficiency of the unmodified based NiO x device.…”

“…Reproduced with permission. [ 135 ] Copyright 2019, Springer. e) Linking NiO x to perovskite layer through pyridine‐terminated conjugated SAMs and the effect of SAMs modification on the hysteresis of PSCs.…”

“…Recently, Mangalam et al. [ 135 ] used 4‐bromobenzylphosphonic acid‐based SAMs for NiO x p‐i‐n PSCs, Figure 8d. The V oc increased from 0.978 to 1.029 V, leading to improved device performance and reduced J – V hysteresis.…”

“…They attribute the increased V oc to a deeper valence band energy of NiO after SAM modification. [ 135 ] Similarly, Zhang et al. [ 136 ] utilized ferrocenedicarboxylic acid (FDA) for NiO surface modification, improving the device performance from 15.13% to 18.20%, along with increasing the UV stability and eliminate J – V hysteresis.…”