Chen Weijie

This study investigates the impact of chloride, bromide, or diiodooctane on the perovskite ink wetting properties, as well as the storage of the substrates. All of the inner layer is inkjet‐printed and annealed at low temperature. This leads to the successful demonstration of 10.7% efficient chlorine‐doped methylammonium lead iodide solar cells.

Considering the recent advances in the fundamental understanding of perovskite devices as well as in the demonstration of larger stability under working conditions, specific attention has still to be paid for their processing for low‐cost applications. Here, the successful demonstration of 10.7% efficient chlorine‐doped methylammonium lead iodide (CH₃NH₃PbI_3‐xCl_x) solar cells based on a fully inkjet‐printed processed under ambient conditions and at low temperature (<90 °C) is reported. A huge hysteresis is observed and the efficiency drops down to 6.4% for the forward scan. The Owens–Wendt–Rabel and Kaelble model is applied to investigate the impact of chloride, bromide, or diiodooctane on the perovskite ink wetting properties. A low surface energy of the substrate provokes dewetting during the perovskite printing. The use of chlorine or bromide tends to increase the wettability of the perovskite ink, improving the impregnation of the ink in porous materials. This work shows the critical importance of properly storing these substrates prior to active layer deposition, in order to produce homogenous layers by inkjet‐printing. The successful printing of all inner layers, excluding bottom and top electrodes, in ambient atmosphere is an additional step toward their expected development at a larger scale by the printed electronic industry.

Perovskite solar cells produced by roll‐to‐roll (R2R) slot die coating on flexible substrates at ambient atmosphere from nontoxic solvents demonstrate an average stabilized efficiency of 12%, with the best value of 13.5%. This study is the first public demonstration of R2R slot die coating of perovskites on 30 cm wide substrates with the deposition and drying speed of 3–5 m min⁻¹.

Abstract

The feasibility of upscaling the perovskite solar cells technologies to high volume production using roll‐to‐roll (R2R) slot die coating is demonstrated in this study. Perovskite solar cells are produced by R2R slot die coating on flexible substrates with a width of 30 cm and the web speed of 3–5 m min⁻¹. R2R deposition of the electron transport layer and perovskite is performed at ambient atmosphere from nontoxic solvents compatible with industrial manufacturing. The average stabilized power conversion efficiency of the devices made on different areas of the foil is 12%, with the best value of 13.5%. The demonstrated achievement is an important milestone and a big solid step toward future commercialization of perovskite‐based solar cells technologies.

A diboron‐assisted strategy for tuning interfacial defects in formamidinium‐iodide‐based perovskite solar cells is demonstrated to decompose the unreacted organic‐halide species at the surface by coating B₂Cat₂ on top of the perovskite films, which can suppress the nonradiative recombination loss and boost power conversion efficiency. This approach paves a new way for mitigating defects and improving device performance.

Abstract

Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)‐based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron‐assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C₁₂H₁₀B₂O₄) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole‐extraction layer is mitigated considerably after the introduction of the proposed approach and charge‐carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance.

An environment‐friendly ammonium thioglycolate‐based aqueous solution process is exploited to successfully deposit as‐prepared Cu₂ZnSnS₄ films in ambient air. It is found that sinstering in ambient air is as good as in argon, making the fabrication process more affordable and reproducible. The low level of Ag doping (Cu_1−x,Ag_x)₂ZnSn(S,Se)₄ solar cells based on this green, low‐cost, and simple synthetic route shows a power conversion efficiency of 7.38%.

Environment‐friendly process, low production cost, and simple operation are regarded as key factors for scalable kesterite photovoltaic applications. Herein a green ammonium thioglycolate (TGAm)‐based aqueous solution route has been developed to deposit Cu₂ZnSnS₄ films. It is found that sinstering in ambient air is as good as in argon, making the production process more affordable and reproducible. TGAm is more active than other alkylthiols with longer alkyl chains and has a strong coordination capability toward metal ions, which is a key factor in the dissolution of a series of metal oxides. Meanwhile, TGAm is widely used in biopharmaceuticals and hairspray, demonstrating good biological compatibility. Moreover, a low level of Ag doping can be successfully incorporated into the host lattice of the CZTSSe to form a homogeneous (Cu_1−x,Ag_x)₂ZnSn(S,Se)₄ (CAZTSSe) alloy material by this aqueous process. Benefiting from the effect of Ag doping, the initial power conversion efficiency is successfully enhanced from 5.86% (x = 0) to 7.38% (x = 2%).

By using chloroform‐assisted HCl method, smooth and full coverage MAPbI₃ films are obtained at room temperature under ambient air condition (relative humidity, 30%). A maximum efficiency of 17.72% is achieved for the MAPbI₃ solar cells fabricated via this method. Good reproducibility is demonstrated for the MAPbI₃ solar cells when relative humidity during device fabrication is between 0% and 30%.

Abstract

The power conversion efficiency of perovskite solar cells has been boosted rapidly, it has so far exceeded that of commercial polycrystalline silicon solar cells. This has prompted great interest in large‐scale production and deployment of perovskite solar cells. However, state‐of‐the‐art perovskite solar cells are fabricated inside gloveboxes and further annealing at high temperatures (typically at >100 °C for 30 min) is needed. These two required conditions are not compatible with, either in the respect to high‐throughput or thermal budget, a feasible industrial production process. By eliminating the two requirements, the deposition of perovskite films both at room temperature and under ambient air condition will make the scalable roll‐to‐roll fabrication scheme feasible. Here, the anti‐solvent (chloroform) washing is introduced to the previously developed hydrochloride‐assisted method and demonstrate that the room‐temperature method can be carried out under ambient air condition for MAPbI₃ film deposition. Through this new procedure, a power conversion efficiency as high as 17.72% is achieved for MAPbI₃ planar devices fabricated under a relative humidity of 30% at room temperature. Further, it is revealed that the room‐temperature process MAPbI₃ films show a near monoexponential decay pathway with a long photoluminescence lifetime of >400 ns.

Publication date: 19 December 2018

Source: Joule, Volume 2, Issue 12

Author(s): Fei Wang, Xianyuan Jiang, Hao Chen, Yuequn Shang, Hefei Liu, Jingle Wei, Wenjia Zhou, Hailong He, Weimin Liu, Zhijun Ning

Context & Scale

Summary

Graphical Abstract

Double cation substitution in Cu₂ZnSnS₄ (CZTS) by partially substituting Cu with Ag and Zn with Cd is shown to alter the characteristics of acceptor defects and deep defects responsible for non‐radiative recombination. This synergistic effect of Cd and Ag reflects in power conversion efficiency of 10.1% (10.8% active area) obtained in the (Cu,Ag)₂(Zn,Cd)SnS₄ system.

Abstract

The performance of many emerging compound semiconductors for thin‐film solar cells is considerably lower than the Shockley–Queisser limit, and one of the main reasons for this is the presence of various deleterious defects. A partial or complete substitution of the cations presents a viable strategy to alter the characteristics of the detrimental defects and defect clusters. Particularly, it is hypothesized that double cation substitution could be a feasible strategy to mitigate the negative effects of different types of defects. In this study, the effects of double cation substitution on pure‐sulfide Cu₂ZnSnS₄ (CZTS) by partially substituting Cu with Ag, and Zn with Cd are explored. A 10.1% total‐area power conversion efficiency (10.8% active‐area efficiency) is achieved. The role of Cd, Ag, and Cd + Ag substitution is probed using temperature‐dependent photoluminescence, time‐resolved photoluminescence, current–voltage (IV), and external quantum efficiency (EQE) measurements. It is found that Cd improves the photovoltaic performance by altering the defect characteristics of acceptor states near the valence band, and Ag reduces nonradiative bulk recombination. It is believed that the double cation substitution approach can also be extended to other emerging photovoltaic materials, where defects are the main culprits for low performance.