Manganese Dopant-Induced Isoelectric Point Tuning of ZnO Electron Selective Layer Enable Improved Interface Stability in Cesium–Formamidinium-Based Planar Perovskite Solar Cells

Abstract

The higher basicity and uncontrolled defect states in the planar zinc oxide (ZnO) electron selective layer (ESL) cause rapid deprotonation of the perovskite absorber which results in higher interface charge recombination at the perovskite/ESL interface restricting the usage of ZnO as the ESL in perovskite solar cells. In this work, the isoelectric point (IEP) of ZnO was tuned by introducing a manganese (Mn4+) dopant in ZnO for the first time. The higher oxidation state of the Mn dopant reduces the basicity of the doped ZnO ESL and controls the perovskite deprotonation at the Mn:ZnO/perovskite interface. The doping of Mn4+ in ZnO results in the generation of two free electrons causing higher conductivity of Mn:ZnO films. The dual effect of a lower IEP and higher conductivity of the Mn:ZnO film along with its improved n-type behavior results in higher surface photovoltage and reduced trap-filled limited voltage (V TFL), which resulted in a higher open-circuit voltage (V oc) (0.92 to 0.99 V). The negligible PbI2 formation at the Mn:ZnO/perovskite interface, lower leakage current (1 order lower than that of ZnO), and a comparatively reduced diode ideality factor (n id) validate the improvement of perovskite/interface stability. The above-mentioned merits of the Mn-doped ZnO-based ESL improved the mixed-cation perovskite power conversion efficiency from 11.7 to 13.6%, which is ∼15% higher than that of a bare ZnO-based ESL. Furthermore, a considerably improved device stability of over 100 h under high relative humidity condition (RH >70%) was observed for the Mn-doped ZnO ESL without any encapsulation.

Critical role of dopant in NiOx hole transport layer for mitigating redox reactivity at NiOx/absorber interface in mixed cation perovskite solar cells

“…The high temperature heat treatment necessary to create the NiO x layer also negatively affects the ITO substrate because it causes R sheet to increase by 8-10 times (from 20 Ω cm −2 to 200 Ω cm −2 ), seriously impairing the device performance by increasing R s , which lowers FF and, in turn, PCE. 34 The increase in V OC is consistent with the increase in work function found in V doped NiO x . Close to 350 meV decrease in contact potential increased the work function of V:NiO x to 5.09 eV which is in agreement with the increase in V OC observed.…”

“…We have previously shown that introducing a hard acid Mn 4+ in the ZnO electron selective layer can significantly reduce its isoelectric point from 9.5 (pristine ZnO) to 8.2 (Mn doped ZnO), thereby suppressing the interface perovskite deprotonation reaction. 34 Since the surface of metal oxide contacts has a universal nature of exhibiting acid–base coupled redox reactions, the above trend observed in the case of Mn doped ZnO will hold true for V doped NiO x as well.…”

“…The high temperature heat treatment necessary to create the NiO x layer also negatively affects the ITO substrate because it causes R sheet to increase by 8–10 times (from 20 Ω cm −2 to 200 Ω cm −2 ), seriously impairing the device performance by increasing R s , which lowers FF and, in turn, PCE. 34…”

Core/Shell ZnO/ZnS Nanoparticle Electron Transport Layers Enable Efficient All‐Solution‐Processed Perovskite Light‐Emitting Diodes

“…[41] As already mentioned above, well-documented instability of metal halide perovskites in contact with polar solvents can result in a rapid decomposition of perovskite films and thus deteriorate electroluminescent (EL) performance of solutionprocessed PeLEDs. [42,43] To prevent this, orthogonal solvent chlorobenzene was used for the dispersion of ZnO and ZnO/ZnS NPs to avoid the negative effect of polar solvents on the lightemitting perovskite layer. To explore the expected stabilizing effect of the ZnO/ZnS on perovskite films, the PL and timeresolved PL (TRPL) spectra (shown in Figure 4a,b, respectively) of the pristine perovskite, perovskite/ZnO NP, and perovskite/ (ZnO/ZnS NP) films on quartz were measured and analyzed.…”

A New Vinylene-Thiophene-Vinylene Linked Triphenylamine-Phenothiazine Unsymmetrical D-π-D Small Molecule: Defect Passivation and Hole Transporting Interfacial Layer for Perovskite Solar Cells

“…The perovskite absorber solution (FA 0.9 Cs 0.1 PbI 3 ) was spin-coated onto the ETL layer using a two-step spin-coating technique at 1000 rpm for 10 s and 4500 rpm for 30 s. 300 μL of anhydrous CB was dripped during the last 8 s of the spin coating, and the film was kept for annealing (20 min). Spiro-OMeTAD precursor solution was later spin-coated on the absorber layer at 3000 rpm for 30 s. Finally, a silver metal (Ag) with a thickness of 100 nm was thermally evaporated at < ∼2 × 10 –6 mbar to complete the device whose active area, designated by a shadow mask, is 3 mm × 3 mm. − …”