Zhenxiao Pan

2D/3D perovskite heterojunctions can effectively passivate surface defects of perovskite films and improve device performance. However, the 2D perovskite formed on the complex surfaces of 3D perovskite is typically randomly oriented, limiting the effect of defect passivation and impeding charge transport. Achieving vertically oriented 2D perovskite on 3D perovskite remains a significant challenge. In this work, we propose a chemical polishing strategy to construct vertically oriented 2D perovskite. By a pre‐transformation chemical polishing design, the impurities on the surface, including residual PbI ₂ and FAI, can be simultaneously removed. This achieves a “clean” surface environment on 3D perovskite, providing an ideal template for subsequent 2D perovskite formation. This strategy realizes the formation of vertically oriented 2D perovskites on the surface of 3D perovskites by the solution approach. The 2D/3D perovskite heterojunction constructed through this polishing route exhibits lower defect states and enhanced charge extraction capability. This strategy increases the efficiency of hole transport layer‐free carbon‐based perovskite solar cells to a new record of 21.36%. The operational stability of the device is also improved.

Improving the crystalline quality of perovskite films is the most effective approach for constructing high‐performance carbon‐based perovskite solar cells (C‐PSCs). In particular, highly (100)‐oriented monolayer perovskite films can effectively suppress defect‐induced recombination while enhancing charge transport, thereby reducing non‐radiative recombination losses in C‐PSCs. In this work, we propose a scalable strategy for constructing a Pb‐rich modified buried interface with abundant Pb sites, which promotes perovskite nucleation and induces an upward unidirectional crystallization process, resulting in large‐grained, (100)‐oriented perovskite films. Moreover, the Pb‐rich interface layer of Pb ₁₀ (PO ₄ ) ₆ O exhibits better lattice matching with perovskite, significantly alleviating interfacial lattice strain at the buried interface. As a result, the fabricated C‐PSCs achieved a champion efficiency of 21.56%, as well as an efficiency of 18.12% for the carbon‐based mini‐module (10.08 cm ² ), which is among the best reported efficiencies for hole transport layer‐free planar C‐PSCs. In addition, the maximum power point tracking of unencapsulated devices offered an outstanding T ₉₀ lifetime exceeding 1000 h under the ISOS‐L‐1I standard protocol. These results confirm that the above strategy possesses excellent scalability and strong potential for large‐area perovskite photovoltaics.

Tin dioxide (SnO ₂ ) electron transport layer (ETL) has become the most commonly used ETL in perovskite solar cells due to its excellent photoelectronic properties. Chemical bath deposition (CBD) is a common method for preparing SnO ₂ ETL. However, the main challenge for this method is the poor reproducibility. Clarifying the key mechanisms that affect the growth of SnO ₂ during the CBD process is crucial for building high‐quality and highly reproducible SnO ₂ ETL. In this work, it is identified that the intrinsic limitations in SnO ₂ ETL performance and reproducibility stem from the competitive coexistence of homogeneous and heterogeneous nucleation pathways. To address this challenge, a pre‐nucleation strategy to enable single heterogeneous nucleation‐driven SnO ₂ deposition is proposed. This is achieved by employing a pre‐nucleated precursor solution that has already undergone homogeneous nucleation for the deposition of SnO ₂ ETL. The resultant ETL exhibits ultrathin conformality, high surface coverage, uniform thickness, and reduced defect‐state density. This strategy not only enhances device performance but also significantly improves process reproducibility. Consequently, the hole transport layer‐free carbon‐based perovskite solar cells achieve a record efficiency of 21%. Furthermore, the device demonstrates remarkable operational stability, retaining 98% of the initial efficiency after 1600 h of continuous maximum power point operation.

High loading of quantum dots (QDs) on TiO₂ photoanode is essential for high power conversion efficiency (PCE) for quantum dot‐sensitized solar cells (QDSCs). However, there remains a large portion (≈60%) of TiO₂ substrate uncovered by QDs, which results in insufficient light harvesting and the undesired charge recombination, consequently suppressing the enhancement of performance in QDSCs. Herein, a convenient and effective method for improving QD loading is proposed, wherein a direct deposition (DA) mode is carried out after a chemical deposition of capping ligand‐induced self‐assembly (CLIS). It is found that the DA compared with CLIS modes leads to different adsorption behaviors and the interactions of QDs with TiO₂ substrate, thus additional QDs can be successfully deposited. The elevated QD loading amount enhances the light‐harvesting capability and effectively inhibits undesired charge recombination at the photoanode/electrolyte interfaces. Consequently, the average PCE is boosted to 16.89% from the pristine 14.95%, and a champion PCE of 17.04% is achieved, which is the new record for liquid‐junction QDSCs.

Hole transport layer (HTL)‐free carbon‐based perovskite solar cells (C‐PSCs) own outstanding potential for commercial applications due to their attractive advantages of low cost and superior stability. However, the abundant defects and mismatched energy levels at the interface of the perovskite/carbon electrode severely limit the device efficiency and stability. Constructing a 2D layer on the surface of 3D perovskite films to form 2D/3D heterojunctions has been demonstrated to be an effective method of passivating surface defects and optimizing the energy level alignment in almost all kinds of PSCs. Due to the unique structure of HTL‐free C‐PSCs, 2D/3D heterojunctions play especially important roles. This review article summarizes the reports of 2D/3D perovskite heterojunctions in HTL‐free C‐PSCs. It describes the contributions of 2D/3D heterojunctions in terms of their roles in defect passivation, energy level optimization, and stability improvement. Finally, challenges and prospects of 2D/3D heterojunction for further development of HTL‐free C‐PSCs are highlighted.

Interface engineering strategies passivate defects on the polycrystalline perovskite film surface and improve the stability of corresponding perovskite solar cells (PSCs). However, a single interface engineering step can result in restricted benefits on various occasions. Therefore, an appropriate additional modification step can be necessary to synergistically improve the device performance. In this study, a two-step interface engineering strategy is developed. Initially, the CsPbI₃ perovskite surface is modified by choline iodide (ChI) to construct a 1D ChPbI₃/3D CsPbI₃ heterojunction, and then an additional surface modification step with the use of crown ether is applied. The crown ether modification can further eliminate unpassivated surface defects after heterojunction construction. Benefiting from the inhibited interfacial recombination, the resultant carbon-electrode-based CsPbI₃ PSCs (C-PSCs) deliver a champion efficiency of 18.78%, representing one of the highest levels in this field. Besides, crown ether can synergistically improve the stability of the device against moisture, heat, and light stress due to the enhanced hydrophobicity and suppressed ion migration.

Two‐step sequential deposition is a widespread technique for the fabrication of perovskite films, renowned for its better control of the crystallization process. However, achieving a well‐controlled and complete reaction of PbI₂ by organic ammonium salts remains a key challenge. Previous studies have predominantly focused on regulating the properties of the PbI₂ layer while paying less attention to the high reactivity of organic ammonium salts. In this study, the natural molecule anethole is first explored to control perovskite crystallization during two‐step sequential deposition, focusing on the reactivity modulation of organic formamidine ion (FA⁺). It is demonstrated that FA⁺ exhibits strong hydrogen bond interactions with anethole, inhibiting the high reactivity of FA⁺ and effectively delaying the rapid reaction between FAI and PbI₂. This decelerates the crystallization kinetics of perovskite films, facilitating the orderly and complete reaction of PbI₂ by FAI while suppressing detrimental δ‐phase formation. Consequently, FA‐based perovskite films with high crystallinity, preferred orientation, and low defect state density are obtained. The fabricated planar hole transport layer‐free carbon electrode perovskite solar cells deliver an efficiency of 20.41% (certified efficiency of 20.0%), which is a new record for this kind of solar cell.