Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Abstract

Nickel oxide (NiO x ) (deposited by sputtering (sp)) is a promising hole transport layer (HTL) for inverted planar perovskite solar cells. However, poor CH 3 NH 3 PbI 3 crystallization, elimination of CH 3 NH 3 + , and formation of residual PbI 2 grains, induced by defects present on the surface of sp-NiO x , have limited the device efficiency. Herein, a facile approach is reported to passivate the surface defects in sp-NiO x and simultaneously induce complete perovskite crystallization (without residual PbI 2 grains) via modifying the sp-NiO x /CH 3 NH 3 PbI 3 interface with various alkali metal halide salts (AMHSs). Comprehensive film and device characterizations reveal the additional influence of AMHSs, especially cesium bromide (CsBr), on the structural, morphological, photophysical, and photovoltaic performance. It is found that incorporation of a CsBr interlayer significantly improves the perovskite crystallization, producing high-quality MAPbI 3 films with enlarged grain sizes (without any residual PbI 2 grains) contrasting without the CsBr-interlayer case. CsBr (and other AMHSs) additionally reduces the band tail states and passivates the surface defects in sp-NiO x (as revealed by X-ray photoelectron spectroscopy and photodeflection spectroscopy), thereby suppressing interfacial disorder and recombination centers and improving the overall charge collection property across the sp-NiO x /CH 3 NH 3 PbI 3 interface. This leads to improvement in the device efficiency (with active area = 1 cm 2 ) and long-term operational stability at the maximum power point under continuous illumination for 8000 s and against ambient atmosphere for ∼2200 h. On the basis of the results, a possible crystallization process is discussed which provides insights into the engineering of the sp-NiO x /CH 3 NH 3 PbI 3 interface rendering improved device performance.

Fully Textured, Production‐Line Compatible Monolithic Perovskite/Silicon Tandem Solar Cells Approaching 29% Efficiency

“…With 2PACz introduced, the binding energy of Ni 2p for Ni 2+ shifts from 853.75 to 854.38 eV. The same trend also occurs to the binding energy of Ni 2p at ≈856 eV for Ni 3+ that corresponds to either Ni 2 O 3 or NiOOH, [33,34] while O 1s peaks also exhibit a shift in We also found evidence suggesting the existence of NiO x that enhanced the adsorption of 2PACz compared to that on bare ITO surface. By washing the NiO x /2PACz and ITO/2PACz films with ethanol, which can well dissolve 2PACz, we observed a more significant drop in phosphorus (P) content from the ITO/2PACz film by calculating the relative residual areas of the P 2p peaks after washing (Figure 2c).…”

“…With 2PACz introduced, the binding energy of Ni 2p for Ni 2+ shifts from 853.75 to 854.38 eV. The same trend also occurs to the binding energy of Ni 2p at ≈856 eV for Ni 3+ that corresponds to either Ni 2 O 3 or NiOOH, [ 33,34 ] while O 1s peaks also exhibit a shift in line with Ni 2p (531.2 and 529.2 eV for O bonded with different Ni species, respectively). The shift in the binding energy of these core‐level peaks indicates a strong coordination between NiO x and 2PACz due to binding between PA group and surface hydroxyl groups of the NiO x , via forming strong PO…Ni or PO…Ni bonds.…”

Charge Carrier Recombination at Perovskite/Hole Transport Layer Interfaces Monitored by Time-Resolved Spectroscopy

“…Additionally, the TA measurements reveal bulk recombination at longer time scales. For the case of sputtered NiO x , our findings concerning the nonradiative recombination are in line with earlier reports in the literature showing that interface passivation improves device performance in NiO x -based devices. , …”

“…For the case of sputtered NiO x , our findings concerning the nonradiative recombination are in line with earlier reports in the literature showing that interface passivation improves device performance in NiO x -based devices. 24,25 The interfacial recombination depends not only on the defect density at the interface but also on the conduction band offset (CBO) and valence band offset (VBO) between the electron transport layer (ETL)/PVK and HTL/PVK interfaces (i.e., PTAA's highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)), which are both supported by simulations and experimentally verified. 26,27 In particular, it was demonstrated that the VB and/or HOMO of the HTL is lower than that of the perovskite absorber; an energy cliff is formed at the interface leading to the accumulation of holes.…”

NiN-Passivated NiO Hole-Transport Layer Improves Halide Perovskite-Based Solar Cell

“…Earlier attempts to passivate the NiO x /HaP interface have improved PSC efficiency and stability. − Most passivation techniques have so far included deposition of a buffer layer through spin coating , or introducing additives into the HaP solution . These passivation approaches are not suited for the fabrication of larger area perovskite devices that would inevitably need solvent-less methods, for both active layer deposition and interface modification. , …”