Organometallic halide perovskite films with good surface morphology and large grain size are desirable for obtaining high‐performance photovoltaic devices. However, defects and related trap sites are generated inevitably at grain boundaries and on surfaces of solution‐processed polycrystalline perovskite films. Seeking facial and efficient methods to passivate the perovskite film for minimizing defect density is necessary for further improving the photovoltaic performance. Here, a convenient strategy is developed to improve perovskite crystallization by incorporating a 2D polymeric material of graphitic carbon nitride (g‐C3N4) into the perovskite layer. The addition of g‐C3N4 results in improved crystalline quality of perovskite film with large grain size by retarding the crystallization rate, and reduced intrinsic defect density by passivating charge recombination centers around the grain boundaries. In addition, g‐C3N4 doping increases the film conductivity of perovskite layer, which is beneficial for charge transport in perovskite light‐absorption layer. Consequently, a champion device with a maximum power conversion efficiency of 19.49% is approached owing to a remarkable improvement in fill factor from 0.65 to 0.74. This finding demonstrates a simple method to passivate the perovskite film by controlling the crystallization and reducing the defect density.
Exploiting organic/inorganic hybrid perovskite solar cells (PSCs) with reduced Pb content is very important for developing environment-friendly photovoltaics. Utilizing of Pb-Sn alloying perovskite is considered as an efficient route to reduce the risk of ecosystem pollution. However, the trade-off between device performance and Sn substitution ratio due to the instability of Sn is a current dilemma. Here, for the first time, the highly efficient Pb-Sn-Cu ternary PSCs are reported by partial replacing of PbI with SnI and CuBr . Sn substitution results in a redshift of the absorption onset, whereas worsens the film quality. Interestingly, Cu introduction can passivate the trap sites at the crystal boundaries of Pb-Sn perovskites effectively. Consequently, a power conversion efficiency as high as 21.08% in inverted planar Pb-Sn-Cu ternary PSCs is approached. The finding opens a new route toward the fabrication of high efficiency Pb-Sn alloying perovskite solar cells by Cu passivation.
Modification of TiO2 by using fullerenes is an efficient strategy to further improve the device efficiency and enhance the cell stability of perovskite solar cells (PSCs). However, the intrinsic issues of low electron mobility and electrical conductivity of fullerene materials may restrict their potential application in PSCs. Here, we demonstrated an n-doped electron-transporting layer by doping bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C62 (bis-PCBM) with decamethylcobaltocene (DMC) to fabricate n–i–p structure PSCs. We successfully realized an n-type doping of bis-PCBM via a solution-processed doping process. DMC doping played a series of roles in adjusting the energy levels, improving the electron mobility and enhancing the film conductivity of bis-PCBM. A bis-PCBM:DMC composite film could act as an underlay for the deposition and growth of a subsequent perovskite layer owing to its smooth morphology. In addition, the bis-PCBM:DMC composite film also presented good solvent resistance, which could slow down the degradation process of the perovskite layer. Consequently, a champion device with a maximum PCE of 20.14% was approached.
Great efforts toward developing novel and efficient hole‐transporting materials are needed to further improve the device efficiency and enhance the cell stability of perovskite solar cells (PSCs). The poor film conductivity and the low carrier mobility of organic small‐molecule‐based hole‐transporting materials restrict their application in PSCs. This study develops an efficient and stable hole‐transporting material, tetrafluorotetracyanoquinodimethane (F4‐TCNQ)‐doped copper phthalocyanine‐3,4′,4′′,4′′′‐tetra‐sulfonated acid tetra sodium salt (TS‐CuPc) via a solution process, in planar structure PSCs. The p‐type‐doped TS‐CuPc film demonstrates improved film conductivity and hole mobility owing to the strong electron affinity of F4‐TCNQ. By the F4‐TCNQ tailoring, the composite film gives the highest occupied molecular orbital level as high as 5.3 eV, which is beneficial for hole extraction. In addition, the aqueous solution processed TS‐CuPc:F4‐TCNQ precursor is almost neutral with good stability for avoiding the electrode erosion. As a result, the fabricated PSCs employing TS‐CuPc:F4‐TCNQ as the hole‐transporting material exhibit a power conversion efficiency of 16.14% in a p–i–n structure and 20.16% in an n–i–p structure, respectively. The developed organic small molecule of TS‐CuPc provides the diversification of hole‐transporting materials in planar PSCs.
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