Thiourea-Assisted Facile Fabrication of High-Quality CsPbBr3 Perovskite Films for High-Performance Solar Cells

Bulk and surface defect manipulation of the ZnO ETL for all-inorganic CsPbBr3 perovskite solar cells

The electron transport layer (ETL) in traditional CsPbBr3 perovskite solar cells (PSCs) without a hole transport layer (HTL) presents the capability to transport electrons and block hole transport, which radically affects the photovoltaic performance of PSCs. However, ZnO ETL prepared using the classic sol-gel method exhibits obvious drawbacks, such as serious interfacial recombination reactions, inducement of oxygen vacancies (VO) and zinc interstitials (Zni). Herein, we demonstrate that alkali metal chloride (e.g. KCl), serving as the passivating agent for the surface and bulk phase, can promote surface modification and doping in the ZnO ETL, respectively. Experimental results show that the interaction between K+ and Zn2+, and the occupation of VO by Cl-, suppresses the internal defect states of the ZnO films, which enhances the crystal coordination between ZnO and CsPbBr3 and improves the film morphology and the quality of the upper perovskite (PVK) films. Experimental PSCs based on the doping approach achieved the highest power conversion efficiency (PCE) of 9.22%, which ranks the highest PCE of the (FTO/ITO)/ZnO/CsPbBr3/carbon structure. Moreover, the unpackaged devices of the two experimental PSCs could maintain 97.15% and 74.76% of the original PCE after being exposed for 28 days in the ambient environment, demonstrating the powerful effect of KCl on the regulation of surface and bulk phase defects in the ZnO ETL.

Methanol as an anti-solvent to improve the low open-circuit voltage of CsPbBr3 perovskite solar cells prepared with water

CsPbBr3 has received more and more attention in the field of optoelectronic devices due to its excellent stability. To address the cost and environmental concerns associated with the use of toxic methanol, water has been explored as a substitute solvent for CsBr in the preparation of CsPbBr3 perovskite solar cells (PSCs). In this study, we utilized methanol as an anti-solvent of the CsBr/H2O solution to regulate the detrimental effects of water on the CsPbBr3 film and control the crystallization process. From results of the experiment, it was found that methanol anti-solvent treatment greatly improved the crystallization of the CsPbBr3 film, increased the grain size, and reduced the defect density. After the introduction of methanol anti-solvent treatment, the power conversion efficiency (PCE) increased from 6.09% to 7.91%, while the open-circuit voltage (Voc) increased from 1.18 V to 1.39 V. Furthermore, we incorporated 2-hydroxyethylurea into the CsPbBr3 PSCs to improve the wettability of PbBr2 towards the CsBr/H2O solution and ensure the formation of pure-phase CsPbBr3 films. The introduction of 2-hydroxyethylurea resulted in an additional increase in Voc from 1.19 V to 1.42 V. The PCE further improved from 6.56% to 8.62% after methanol anti-solvent treatment. These results demonstrate that methanol treatment effectively addresses the low Voc issue observed in CsPbBr3 PSCs prepared with water as a solvent. Importantly, this approach significantly reduces the reliance on methanol compared to conventional fabrication methods for CsPbBr3 PSCs. Overall, this work presents a promising pathway for achieving high Voc and efficiency in CsPbBr3 PSCs by utilizing water as a solvent.

Enhanced Photoelectric Properties of CsPbBr3 by SiO2 and TiO2 Bilayer Heterostructures

CsPbBr3/SiO2 heterostructures were synthesized by the hydrolysis reaction of a mixture of CsPbBr3 nanocrystals (NCs) and (3-aminopropyl)triethoxysilane (APTS) in air. Compared with CsPbBr3 NCs, the CsPbBr3/SiO2 heterostructures exhibit stronger photoluminescence (PL) intensity, longer lifetime of PL (∼40.5 ns), and higher PL-quantum yield (PLQY, ∼86%). The carrier dynamics of CsPbBr3/SiO2 was detected by the transient absorption (TA) spectrum. The experimental results show that SiO2 passivates the surface traps of CsPbBr3 NCs and enhances the PL intensity. However, photoelectrochemical impedance spectra (PEIS) demonstrate that the impedance of CsPbBr3/SiO2 is higher than that of CsPbBr3 NCs, which reduces carrier transport and extraction. Because the application of CsPbBr3/SiO2 in optoelectronics is limited, CsPbBr3/SiO2/TiO2 heterostructures were synthesized by the further reaction of tetrabutyl titanate (TBT). The TiO2 coating can reduce the impedance of the CsPbBr3/SiO2. Importantly, ∼68% of the PL intensity of CsPbBr3/SiO2 is retained. Compared with CsPbBr3/SiO2 and CsPbBr3 NCs, the CsPbBr3/SiO2/TiO2 demonstrates faster carrier transport (κct = 2.4 × 109 s-1) and higher photocurrent density (J = 76 nA cm-2). In addition, CsPbBr3/SiO2/TiO2 shows good stability under (ultraviolet) UV irradiation, along with water stability and thermal stability. Therefore, the double protection approach can enhance the stability of CsPbBr3 NCs and tune the optoelectronic properties of CsPbBr3 NCs.

Robust and Efficient Carbon-Based Planar Perovskite Solar Cells with a CsPbBr3-MoS2 Hybrid Absorber

Optical response improvement and hole transport/extraction enhancement are critical to enhancing the power conversion efficiency (PCE) of carbon electrode-based perovskite solar cells (C-PSCs) with an absorber of CsPbBr3. In this study, a multifunctional optimization method by embedding MoS2 nanosheets in CsPbBr3 bulk to construct a perovskite-nanosheet hybrid structure was presented. A CsPbBr3-MoS2 hybrid film was fabricated by two-step spin-coating the precursor solutions of PbBr2 and CsBr-MoS2 under an ambient atmosphere, where the aqueous solution with highly distributed MoS2 nanosheets was applied as a solvent of the hybrid precursor solution. MoS2 nanosheets were utilized as a p-type modifier and extra absorber to hybridize with CsPbBr3 for improving the CsPbBr3-carbon interface and light absorption ability of the perovskite layer. As expected, the optical response ability, absorber film quality, and carrier separation/extraction/transport properties of C-PSCs were enhanced significantly by embedding MoS2 nanosheets in CsPbBr3 film, which resulted in enhanced C-PSCs properties. Finally, the C-PSCs with the structure of FTO/SnO2/CsPbBr3-MoS2/C presented a champion PCE of 7.87% (active area: 1 cm2), which demonstrated excellent ambient and operational stability. This study provides an efficient method for constructing ultrastable C-PSCs by hybridizing perovskite and nanosheets.

Research Progress of Green Solvent in CsPbBr3 Perovskite Solar Cells

In optoelectronic applications, all-Brominated inorganic perovskite CsPbBr₃ solar cells have received a great deal of attention because of their remarkable stability and simplicity of production. Most of the solvents used in CsPbBr₃ perovskite solar cells are toxic, which primarily hinders the commercialization of the products. In this review, we introduce the crystal structure and fundamental properties of CsPbBr₃ materials and the device structure of perovskite cells, summarize the research progress of green solvents for CsPbBr₃ PSCs in recent years from mono-green solvent systems to all-green solvent systems, and discuss the approaches to improving the PCE of CsPbBr₃ PSCs, intending to facilitate the sustainable development of CsPbBr₃ perovskite solar cells. Finally, we survey the future of green solvents in the area of CsPbBr₃ perovskite solar cells.

Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI_3-x Br_x film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm² and 1.0 cm² device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.