Efficient and Stable Tin-Lead Mixed Perovskite Solar Cells Using Post-Treatment Additive with Synergistic Effects.

Inhibiting the oxidation of Sn2+ during the crystallization process of Sn-Pb mixed perovskite film is found to be as important as the oxidation resistance of precursor solution to achieve high efficiency, but less investigated. Considering the excellent reduction feature of hydroquinone and the hydrophobicity of tert-butyl group, an antioxidant 2,5-di-tert-butylhydroquinone (DBHQ) was introduced into Sn-Pb mixed perovskite films using an anti-solvent approach to solve this problem. Interestingly, we find that DBHQ can act as function alterable additive during its utilization. On the one hand, DBHQ can restrict the oxidation of Sn2+ during the crystallization process, facilitating the fabrication of high-quality perovskite film; on the other hand, the generated oxidation product 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) can functionalize as defect passivator to inhibit the charge recombination. As a result, this synergetic effect renders the Sn-Pb mixed PSC a power conversion efficiency (PCE) up to 23.0 %, which is significantly higher than the reference device (19.6 %). Furthermore, the unencapsulated DBQH-modified PSCs exhibited excellent long-term stability and thermal stability, with the devices maintaining 84.2 % and 78.9 % of the initial PCEs after aging at 25 °C and 60 °C for 800 h and 120 h under N2 atmosphere, respectively. Therefore, the functional alterable strategy provides a novel cornerstone for high-performance Sn-Pb mixed PSCs.

Enhancing the Performance of Perovskite Solar Cells via the Functional Group Synergistic Effect in Interfacial Passivation Materials.

Interfacial defects are considered to be a stumbling block in producing highly efficient perovskite solar cells (PSCs), so a more reasonable design is required for interfacial passivation materials (IPMs) to achieve further improvements in PSC performance. Here, we use fluorine atom (-F) and methoxy (-OCH3) functional groups to modify the same molecular fragment, obtaining three kinds of IPMs named YZ-301, YZ-302, and YZ-303, respectively. Through the subtle combination of -F and -OCH3, the fragment in YZ-302 exhibits an enhanced electronegativity, rendering the correlative IPM with a stronger interaction with the perovskite layer. As a result, YZ-302 shows the best defect passivation and hole transport effect at the interface, and the PSC based on YZ-302 treatment achieves the best efficiency approaching 24%, which is better than the reference and devices with other IPMs, and it also has excellent device stability.

An efficient asymmetric structured hole transport material for perovskite solar cells.

Hole transport materials (HTMs) play a crucial role in achieving efficient perovskite solar cells (PSCs). In this work, an HTM MF-ACD with an asymmetric structure is designed by introducing two different peripheral end groups. The asymmetric feature increases the molecular dipole of MF-ACD, and endows MF-ACD with good stability and film formation properties, higher hole mobility and conductivity. Consequently, the MF-ACD-based PSC shows a high efficiency of 23.1%, which is much higher than that of the symmetric counterpart. The results show that the asymmetric configuration might be a potential choice to develop more efficient HTMs.

Crystalline Ni-Fe phosphide/amorphous P doped Fe-(oxy)hydroxide heterostructure as a multifunctional electrocatalyst for solar cell-driven hydrogen production.

Hydrogen production by electrocatalytic water splitting is considered to be an effective and environmental method, and the design of an electrocatalyst with high efficiency, low cost, and multifunction is of great importance. Herein, we developed a crystalline NiFe phosphide (NiFeP)/amorphous P-doped FeOOH (P-FeOOH) heterostructure (defined as P-NiFeOxHy) as a high-efficiency multifunctional electrocatalyst for water electrolysis. The NiFeP nanocrystals provide remarkable electronic conductivity and plenty of active sites, the amorphous P-FeOOH improves the adsorption energy of oxygen-containing species, and the crystalline/amorphous heterostructure with superhydrophilic and superaerophobic surface generates synergistic effects, providing plentiful active sites and efficient charge/mass transfer. Benefiting from this, the designed P-NiFeOxHy displays ultralow overpotentials of 159.2 and 20.8 mV to achieve 10 mA cm-2 for oxygen evolution reaction and hydrogen evolution reaction, and also shows the superior performance of urea oxidation reaction with a low voltage of 1.37 V at 10 mA cm-2 in 1 M KOH with 0.33 M urea. In-situ Raman spectra and ex-situ XPS analysis were also used to investigate the catalytic process and reveal the surface structure evolution of P-NiFeOxHy under electrochemical oxidation. Accordingly, the designed P-NiFeOxHy is employed as both cathode and anode to assemble into the urea-assisted water electrolysis device, which can reach 10 mA cm-2 with a low 1.36 V and could be further driven by a solar cell. The work reveals a design of superior activity, cost-effective and multifunctional electrocatalysts for water splitting.

Asymmetric Small Molecule as Interface "Governor" for FAPbI3 Perovskite Solar Cells.

Delicate interface modification is necessary for improving the photovoltaic performance of a perovskite solar cell (PSC). Herein, two asymmetric small molecules, termed BTD-DA and BTD-PA are designed and synthesized to govern the perovskite/Spiro-OMeTAD interface. The molecule BTD-PA featuring a donor-acceptor-acceptor (D-A-A') configuration shows a larger molecule dipole and a better effect on defect passivation and energy level regulation through the strong interaction between the pyridine group in BTD-PA and the surficial uncoordinated Pb2+. Consequently, the PSCs based on the BTD-PA treatment harvest a champion power conversion efficiency (PCE) of 24.46% for a 0.09 cm2 active area and 22.46% for the 1 cm2 device. Moreover, the long-term stability of FAPbI3 PSCs is also significantly improved because of the enhanced hydrophobicity and the inhibited phase transition of the FAPbI3 film with BTD-PA treatment. Our research provides a new strategy for interfacial engineering to boost the PCE and stability of the FAPbI3 PSCs.

Molecular Engineering of Peripheral Substitutions to Construct Efficient Acridine Core-Based Hole Transport Materials for Perovskite Solar Cells.

The development of highly efficient hole transport materials (HTMs) for perovskite solar cells (PSCs) has been a hot research topic. Acridine and its derivatives are gradually utilized as new blocks for optoelectronic applications, which stems from its rigid conjugated structure, shedding a new light on this old molecule. Meanwhile, its application in PSCs as a HTM has not been well explored, and the efficiency of 9,10-dihydroacridine (ACR)-based HTMs is relatively low. In this work, we conduct a systematic modulation of the peripheral substituents for ACR core building block-based HTMs and investigate the effects of the electron-donating ability and π-conjugation of peripheral groups on the photovoltaic performance of the corresponding HTMs. It is found that the peripheral groups with a weaker electron-donating ability and stronger π-conjugation are more suitable for the acridine core, which itself has a stronger electron-donating ability. Through molecular engineering, the newly developed HTM ACR-PhDM achieves an impressive power conversion efficiency of 23.5%. Our work lays the foundation for the design and development of efficient HTMs in the future.

Bi(trifluoromethyl) Benzoic Acid-Assisted Shallow Defect Passivation for Perovskite Solar Cells with an Efficiency Exceeding 21.

Chemical additive engineering is reported to be a simple yet effective approach to passivate shallow defects at the surface and grain boundaries, restrict nonradiative recombination losses, and further enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, we successfully introduce a small organic molecule 3,5-bis(trifluoromethyl)benzoic acid (6FBzA) into an antisolvent as a shallow defect passivator for perovskite films. The Pb2+ defects at the surface are greatly healed due to the coordination interaction of carbonyl and fluorine groups of 6FBzA with Pb2+. Consequently, the trap-assisted nonradiative recombination is effectively suppressed, as well as the interfacial charge extraction and transfer is significantly enhanced. As a result, the 6FBzA-treated PSC obtains a champion PCE of 21.09% with negligible hysteresis, which is obviously superior to the reference device (18.45%). Furthermore, on account of the high hydrophobicity of 6FBzA, the unencapsulated 6FBzA-treated device exhibits a good long-term stability, maintaining 82% of its initial PCE at a relative humidity of 30-40% in ambient air after 1800 h of aging.