Sodium Dodecylbenzene Sulfonate Interface Modification of Methylammonium Lead Iodide for Surface Passivation of Perovskite Solar Cells

Microstrain and Crystal Orientation Variation within Naked Triple-Cation Mixed Halide Perovskites under Heat, UV, and Visible Light Exposure

The instability of perovskite absorbers under various environmental stressors is the most significant obstacle to widespread commercialization of perovskite solar cells. Herein, we study the evolution of crystal structure and microstrain present in naked triple-cation mixed CsMAFA-based perovskite films under heat, UV, and visible light (1 Sun) conditions by grazing-incidence wide-angle X-ray scattering (GIWAXS). We find that the microstrain is gradient distributed along the surface normal of the films, decreasing from the upper surface to regions deeper within the film. Moreover, heat, UV, and visible light treatments do not interfere with the crystalline orientations within annealed polycrystalline films. However, when subjected to heat, the naked perovskite films exhibit a rapid component decomposition, induced by phase separation and ion migration. Conversely, under exposure to UV and 1 Sun light soaking, the naked perovskite films undergo a self-optimization structure evolution during degradation and develop into smoother films with reduced surface potential fluctuations.

Multifunctional Molecule Assists Passivate Method to Simultaneously Improve the Efficiency and Stability of Perovskite Solar Cells

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been greatly improved recently. However, in organic-inorganic polycrystalline perovskite films many defects inevitably exist, which limits the PCE and stability of PSCs. Herein, a small organic molecule 2-chlorothiazole-4-carboxylic acid (SN) is spin coated on a perovskite film to enhance the performance of PSCs. We find that the multifunctional molecule SN reacts with under-coordinated Pb²⁺ ions and I^- vacancies because of the presence of the sulfur and nitrogen donor atoms, and the -COOH groups, which are conducive to suppressing charge recombination and passivating defects. Even more, the introduction of the SN layer can effectively adjust the energy level alignment, which is conducive to the separation and extraction of charge carriers in PSCs. Therefore, devices with SN modification show a champion PCE of 22.55 %. Besides, PSCs with SN show impressive stability, retaining 96 % of its initial PCE after storage in ambient air for 500 h.

A Sulfonated All-Aromatic Polyamide for Heavy Metal Capture: A Model Study with Pb(II)

Polyelectrolytes are widely used in heavy metal removal, finding applications as coagulants and flocculants. We compare the heavy metal removal capability of a water-soluble sulfonated semirigid polyamide, poly(2,2'-disulfonyl-4,4'-benzidine isophthalamide) (PBDI), with that of a well-known random-coil polymer, poly(sodium 4-styrenesulfonate) (PSS). Using lead (Pb(II)) as a model contaminant, both polymers precipitate out from solution at ~500 mg/L Pb(II) in water. The ability to remove Pb(II) from water was quantified using adsorption isotherms and fitted with Langmuir and Freundlich adsorption models. The sorption of Pb(II) by PSS fit the Langmuir model with a high degree of correlation (0.976 R2), but the sorption of Pb(II) by PBDI could not be accurately predicted using the Langmuir or Freundlich model. The sorption of Pb(II) by PBDI and PSS was compared by normalizing sorption by the number of sulfonate groups of each polymer and the ion exchange capacity (IEC), found by titration. We find that PBDI removes a greater amount of Pb(II) per gram of sorbent compared to PSS, 410 mg/g vs 260 mg/g, respectively, which cannot be accounted for by differences in IEC or number of sulfonate groups. Our findings confirm that the positioning of the sulfonate groups and the rigidity of the polymer backbone play an important role in how Pb(II) coordinates to the polymer prior to precipitating out from solution.

Antisolvent Additive Engineering for Boosting Performance and Stability of Graded Heterojunction Perovskite Solar Cells Using Amide-Functionalized Graphene Quantum Dots

Additive and antisolvent engineering strategies are outstandingly efficient in enhancing perovskite quality, photovoltaic performance, and stability of perovskite solar cells (PSCs). In this work, an effective approach is applied by coupling the antisolvent mixture and multi-functional additive procedures, which is recognized as antisolvent additive engineering (AAE). The graphene quantum dots functionalized with amide (AGQDs), which consists of carbonyl, amine, and long hydrophobic alkyl chain functional groups, are added to the antisolvent mixture of toluene (T) and hexane (H) as an efficient additive to form the CH₃NH₃PbI₃ (MAPI):AGQDs graded heterojunction structure. A broad range of analytical techniques, including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, space charge limited current, UV-visible spectroscopy, external quantum efficiency, and time-of-flight secondary ion mass spectrometry, are used to investigate the effect of AAE treatment with AGQDs on the quality of perovskite film and performance of the PSCs. Importantly, not only a uniform and dense perovskite film with hydrophobic property is obtained but also defects on the perovskite surface are significantly passivated by the interaction between AGQDs and uncoordinated Pb²⁺. As a result, an enhanced power conversion efficiency (PCE) of 19.10% is achieved for the champion PSCs treated with AGQD additive, compared to the PCE of 16.00% for untreated reference PSCs. In addition, the high-efficiency PSCs based on AGQDs show high stability and maintain 89% of their initial PCE after 960 h in ambient conditions.

Bi and Sn Doping Improved the Structural, Optical and Photovoltaic Properties of MAPbI3-Based Perovskite Solar Cells

One of the most amazing photovoltaic technologies for the future is the organic–inorganic lead halide perovskite solar cell, which exhibits excellent power conversion efficiency (PCE) and can be produced using a straightforward solution technique. Toxic lead in perovskite can be replaced by non-toxic alkaline earth metal cations because they keep the charge balance in the material and some of them match the Goldschmidt rule’s tolerance factor. Therefore, thin films of MAPbI₃, 1% Bi and 0%, 0.5%, 1% and 1.5% Sn co-doped MAPbI₃ were deposited on FTO-glass substrates by sol-gel spin-coating technique. XRD confirmed the co-doping of Bi–Sn in MAPbI₃. The 1% Bi and 1% Sn co-doped film had a large grain size. The optical properties were calculated by UV-Vis spectroscopy. The 1% Bi and 1% Sn co-doped film had small E_g, which make it a good material for perovskite solar cells. These films were made into perovskite solar cells. The pure MAPbI₃ film-based solar cell had a current density (J_sc) of 9.71 MA-cm⁻², its open-circuit voltage (V_oc) was 1.18 V, its fill factor (FF) was 0.609 and its efficiency (η) was 6.98%. All of these parameters were improved by the co-doping of Bi–Sn. The cell made from a co-doped MAPbI₃ film with 1% Bi and 1% Sn had a high efficiency (10.03%).

Methylammonium Compensation Effects in MAPbI3 Perovskite Solar Cells for High-Quality Inorganic CuSCN Hole Transport Layers

Recent studies have demonstrated that copper (I) thiocyanate (CuSCN) has huge potential as a hole extraction material (HEM) for perovskite solar cells. Here, we used CuSCN as a HEM and analyzed its relationships with a methylammonium lead iodide (MAPbI₃) perovskite layer. The CuSCN dissolved in diethyl sulfide (DES) was spin-coated on the MAPbI₃ layer. For high-quality and dense CuSCN layers, post-annealing was carried out at various temperatures and times. However, the unwanted dissociation of MAPbI₃ to PbI₂ was observed due to the post-annealing for a long time at elevated temperatures. In addition, DES, which is used as a CuSCN solvent, is a polar solvent that damages the surface of MAPbI₃ perovskites and causes poor interfacial properties between the perovskite layer and HEM. To solve this problem, the effect of the molar ratio of methylammonium iodide (MAI) and PbI₂ in the MAPbI₃ precursor solution was investigated. The excess MAI molar ratio in the MAPbI₃ precursor solution reduced MAPbI₃ surface damage despite using DES polar solvent for CuSCN solution. In addition, dissociation of MAPbI₃ to PbI₂ following an adequate post-annealing process was well suppressed. The excess MAI molar ratio in the MAPbI₃ precursor could be compensated for the MA loss and effectively suppress phase separation from MAPbI₃ to MAI + PbI₂ during post-annealing. The efficiency based on the normal planar structure of CuSCN/MAPbI₃ (using excess MAI)/TiO₂ was approximately 17%. The CuSCN-based MAPbI₃ device shows more optimized stability than the conventional spiro-OMeTAD under damp heat (85 °C and 85% relative humidity) conditions because of the robust inorganic HEM.

A Porphyrin-Involved Benzene-1,3,5-Tricarboxamide Dendrimer (Por-BTA) as a Multifunctional Interface Material for Efficient and Stable Perovskite Solar Cells

Surface defects of perovskite films are the major sources of nonradiative recombination which limit the efficiency and stability of perovskite solar cells. Surface passivation represents one of the most efficient strategies to solve this problem. Herein, for the first time we designed a porphyrin-involved benzene-1,3,5-tricarboxamide dendrimer (Por-BTA) as a multifunctional interface material between the interface of the perovskite and the hole-transporting layer (spiro-OMeTAD) for the surface passivation of perovskite films. The results suggested that Por-BTA not only efficiently passivated the perovskite surface defects via the coordination of the exposed Pb²⁺ with the carbonyl unit and basic sites of pyrrole units in Por-BTA but also improved the interface contact and the charge transfer between the perovskite and spiro-OMeTAD ascribed to the strong intermolecular π-π stacking of Por-BTA. It was shown that the PSC devices with the Por-BTA treatment exhibited improved power conversion efficiency with the champion of 22.30% achieved (21.30% for the control devices), which is mainly attributed to the increased short-circuit current density and fill factor. Interestingly, the stability of moisture for the Por-BTA-treated device was also enhanced compared to those without the Por-BTA treatment. This work presents a promising direction toward the design of multifunctional organic molecules as the interface materials to improve the cell performance of PSCs.

Advent of alkali metal doping: a roadmap for the evolution of perovskite solar cells

Metal–halide hybrid perovskites have prompted the prosperity of the sustainable energy field and simultaneously demonstrated their great potential in meeting both the growing consumption of energy and the increasing social development requirements.