Jianli Wang

Bio: Jianli Wang is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Perovskite (structure) & Materials science. The author has an hindex of 2, co-authored 5 publications receiving 27 citations.

Compositional optimization of a 2D–3D heterojunction interface for 22.6% efficient and stable planar perovskite solar cells

Abstract: The stacking of 2D perovskites on the top of 3D perovskites has been recognized as a promising interfacial treatment approach to improve the stability and efficiency of planar perovskite solar cells (PSCs). However, traditional 2D–3D perovskite heterojunctions obtained from the high-temperature annealing process still exhibit unsatisfactory charge transfer performance and interfacial voltage loss. Herein, we introduce isopentylammonium iodide (PNAI) as the large organic ammonium salt, and adjust the in situ grown processes of 2D perovskites by thermal treatments to form a multi-component capping layer composed of 2D perovskites with plenty of high n-value 2D phases (n ≥ 3, n is the number of inorganic layers) and residual PNAI molecules on 3D perovskites. Such an optimized composition for a 2D–3D perovskite heterojunction can remarkably improve the charge transfer performance, further suppress the interfacial ionic defects, and enlarge Fermi-level splitting, leading to a low bandgap-to-voltage loss (0.38 V). Consequently, this treatment strategy significantly improves the efficiency of planar PSCs to 22.62% with an outstanding open-circuit voltage of 1.16 V. Moreover, the unencapsulated PNAI-90 treated device stored under a relative humidity of 30 ± 5% for 1000 h still retains 89% of its initial PCE. This work offers a new strategy to construct a robust 2D–3D heterojunction for planar PSCs.

Tuning the Interfacial Dipole Moment of Spacer Cations for Charge Extraction in Efficient and Ultrastable Perovskite Solar Cells

Abstract: The two-dimensional (2D)/three-dimensional (3D) heterojunction perovskite solar cell (PSC) has recently been recognized as a promising photovoltaic structure for achieving high efficiency and long-...

Balancing crystallization rate in a mixed Sn–Pb perovskite film for efficient and stable perovskite solar cells of more than 20% efficiency

Abstract: In the journey to obtain well-crystallized mixed tin (Sn)–lead (Pb) iodide perovskite films for solar cell application, great difficulties have been presented due to very different crystallization rates between Sn- and Pb-based perovskite components. Herein, we report a new strategy to grow highly crystallized Sn–Pb perovskite (FA0.7MA0.3Sn0.5Pb0.5I3) for perovskite solar cells (PSCs). An iso-pentylammonium tetrafluoroborate ([PNA]BF4) ionic salt layer is introduced on top of poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) to function as anchoring agent to bond Pb2+ to the surface of PEDOT:PSS, which can facilitate a quick crystallization of Pb-containing perovskite components and homogeneously distribute Sn/Pb elements inside the perovskite film in a vertical direction, uncovered by focused ion beam time-of-flight secondary ion mass spectrometry. Additionally, greatly reduced surface residual stress was also confirmed by X-ray diffraction. Lastly, these ionic salt molecules are able to encapsulate the acidic and hygroscopic surface of PEDOT:PSS to further ensure device stability. As a result, our strategies enabled a champion PCE of 20.11% for mixed Sn–Pb PSCs with improved thermal stability at 85 °C over 240 hours and shelf storage stability over 1200 hours. This work provides a new strategy to regulate the crystallization process of mixed Sn–Pb perovskites for both high performance and stability.

Overcoming the carrier transport limitation in Ruddlesden–Popper perovskite films by using lamellar nickel oxide substrates

Abstract: Quasi two-dimensional (2D) Ruddlesden–Popper perovskites films fabricated by a solution process are composed of multiple 2D perovskite phases, and carrier transportation is limited by low-n-value 2D perovskite phases (n = 1 and n = 2). Systematic characterization shows that BA based 2D perovskites do not form low-n-value phases, while PEA and FPEA based 2D perovskites have strong n = 1, 2 signals when excited from the bottom of the perovskite films. To solve this problem, a lamellar nickel oxide substrate (lamellar-NiOx) fabricated by the hydrothermal method is employed as a hole transporting layer, forming a vertical charge transport pathway at the bottom of perovskite films, thus bypassing the charge trapping and recombination centers of the low-n-value regions of PEA and FPEA based 2D perovskites. As a result, both fill factor and open-circuit voltage are greatly enhanced for PEA and FPEA based 2D perovskite solar cells and a champion power conversion efficiency of 15.2% is achieved with a composition of FPEA2MA3Pb4I13. Furthermore, 2D perovskite films on lamellar-NiOx show enlarged grain size, improved out-of-plane orientation, and enhanced carrier transport efficiency between different n-value 2D perovskite phases. These findings suggest that lamellar-NiOx is an ideal substrate candidate to help overcome the carrier transport limitation of low-n-value 2D perovskite phases near the bottom of perovskite films.

Suppressing Residual Lead Iodide and Defects in Sequential-Deposited Perovskite Solar Cell via Bidentate Potassium Dichloroacetate Ligand.

Abstract: In the sequential-deposited polycrystalline perovskite solar cells, the unreacted lead iodide due to incomplete conversion of lead iodide to perovskite phase, can contribute to ionic defects, such as residual lead ions (Pb 2+ ). At present, passivation of interfacial and grain boundary defects has become an effective strategy to suppress charge recombination. Here, we introduced potassium acetate (KAc) and potassium dichloroacetate (KAcCl 2 ) as additives in the sequential deposition of polycrystalline perovskite thin film and found that acetate ions (Ac - ) can effectively reduce the residual lead iodide. Compared with acetate (Ac), dichloroacetate (AcCl 2 ) can form Pb-Cl and Pb-O bonding as "dual anchoring" bonds with residual Pb 2+ , resulting in strong binding force and effective passivation of residual Pb 2+ defects. Furthermore, potassium ions (K + ) can enlarge grain size and restrain ion migration at the grain boundaries. Consequently, the perovskite solar cell with KAcCl 2 additive shows power conversion efficiency (PCE) from 19.67% to 22.12%, with the open-circuit voltage increased from 1.06 V to 1.14 V. The unencapsulated device can maintain 82% of the initial PCE under a humidity of 30±5% for 1200 hours. This work provides a new approach for the regulation of ionic defects and grain boundaries at the same time to develop high-performance planar perovskite solar cells.

Designs from single junctions, heterojunctions to multijunctions for high-performance perovskite solar cells.

Abstract: Hybrid metal-halide perovskite solar cells (PVSCs) have drawn unprecedented attention during the last decade due to their superior photovoltaic performance, facile and low-cost fabrication, and potential for roll-to-roll mass production and application for portable devices. Through collective composition, interface, and process engineering, a comprehensive understanding of the structure-property relationship and carrier dynamics of perovskites has been established to help achieve a very high certified power conversion efficiency (PCE) of 25.5%. Apart from material properties, the modified heterojunction design and device configuration evolution also play crucial roles in enhancing the efficiency. The adoption and/or modification of heterojunction structures have been demonstrated to effectively suppress the carrier recombination and potential losses in PVSCs. Moreover, the employment of multijunction structures has been shown to reduce thermalization losses, achieving a high PCE of 29.52% in perovskite/silicon tandem solar cells. Therefore, understanding the evolution of the device configuration of PVSCs from single junction, heterojunction to multijunction designs is helpful for the researchers in this field to further boost the PCE beyond 30%. Herein, we summarize the evolution and progress of the single junction, heterojunction and multijunction designs for high-performance PVSCs. A comprehensive review of the fundamentals and working principles of these designs is presented. We first introduce the basic working principles of single junction PVSCs and the intrinsic properties (such as crystallinity and defects) in perovskite films. Afterwards, the progress of diverse heterojunction designs and perovskite-based multijunction solar cells is synopsized and reviewed. Meanwhile, the challenges and strategies to further enhance the performance are also summarized. At the end, the perspectives on the future development of perovskite-based solar cells are provided. We hope this review can provide the readers with a quick catchup on this emerging solution-processable photovoltaic technology, which is currently at the transition stage towards commercialization.

Charge‐Carrier Transport in Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

Abstract: In recent years, 2D Ruddlesden-Popper (2DRP) perovskite materials have been explored as emerging semiconductor materials in solar cells owing to their excellent stability and structural diversity. Although 2DRP perovskites have achieved photovoltaic efficiencies exceeding 19%, their widespread use is hindered by their inferior charge-carrier transport properties in the presence of diverse organic spacer cations, compared to that of traditional 3D perovskites. Hence, a systematic understanding of the carrier transport mechanism in 2D perovskites is critical for the development of high-performance 2D perovskite solar cells (PSCs). Here, the recent advances in the carrier behavior of 2DRP PSCs are summarized, and guidelines for successfully enhancing carrier transport are provided. First, the composition and crystal structure of 2DRP perovskite materials that affect carrier transport are discussed. Then, the features of 2DRP perovskite films (phase separation, grain orientation, crystallinity kinetics, etc.), which are closely related to carrier transport, are evaluated. Next, the principal direction of carrier transport guiding the selection of the transport layer is revealed. Finally, an outlook is proposed and strategies for enhancing carrier transport in high-performance PSCs are rationalized.

Tuning the Interfacial Dipole Moment of Spacer Cations for Charge Extraction in Efficient and Ultrastable Perovskite Solar Cells

Abstract: The two-dimensional (2D)/three-dimensional (3D) heterojunction perovskite solar cell (PSC) has recently been recognized as a promising photovoltaic structure for achieving high efficiency and long-...

Balancing crystallization rate in a mixed Sn–Pb perovskite film for efficient and stable perovskite solar cells of more than 20% efficiency

Abstract: In the journey to obtain well-crystallized mixed tin (Sn)–lead (Pb) iodide perovskite films for solar cell application, great difficulties have been presented due to very different crystallization rates between Sn- and Pb-based perovskite components. Herein, we report a new strategy to grow highly crystallized Sn–Pb perovskite (FA0.7MA0.3Sn0.5Pb0.5I3) for perovskite solar cells (PSCs). An iso-pentylammonium tetrafluoroborate ([PNA]BF4) ionic salt layer is introduced on top of poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) to function as anchoring agent to bond Pb2+ to the surface of PEDOT:PSS, which can facilitate a quick crystallization of Pb-containing perovskite components and homogeneously distribute Sn/Pb elements inside the perovskite film in a vertical direction, uncovered by focused ion beam time-of-flight secondary ion mass spectrometry. Additionally, greatly reduced surface residual stress was also confirmed by X-ray diffraction. Lastly, these ionic salt molecules are able to encapsulate the acidic and hygroscopic surface of PEDOT:PSS to further ensure device stability. As a result, our strategies enabled a champion PCE of 20.11% for mixed Sn–Pb PSCs with improved thermal stability at 85 °C over 240 hours and shelf storage stability over 1200 hours. This work provides a new strategy to regulate the crystallization process of mixed Sn–Pb perovskites for both high performance and stability.