Efficient Mixed‐Cation Mixed‐Halide Perovskite Solar Cells by All‐Vacuum Sequential Deposition Using Metal Oxide Electron Transport Layer

Abstract

The incorporation of various cations and halides to form mixed perovskites has enabled perovskite solar cells (PSCs) to exceed 20% power conversion efficiencies (PCEs). However, they are primarily prepared by solution methods, which limit film uniformity and scalability. Although co‐evaporation is used to prepare all‐vacuum‐deposited PSCs with a decent performance, it involves multiple sources and quartz crystal monitors (QCMs) to simultaneously control deposition rates and film thicknesses, which increase production cost and fabrication complexity and interfere QCMs’ reading precision. Herein, a simple and cost‐effective sequential vapor deposition involving only one QCM and two sources is demonstrated as an advantageous and reliable method to fabricate high‐quality and uniform mixed‐cation mixed‐halide perovskite films with microscale grain sizes and extraordinary morphology for the PSC application. In addition, for the first time, radio frequency (RF)‐sputtered SnO2 is implemented into all‐vacuum‐deposited PSCs as an electron transport layer (ETL). Together with evaporated copper phthalocyanine (CuPc) as a thermally and chemically stable low‐cost hole transport layer (HTL), alternative to the commonly used 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamino)‐9,9′‐spirobifluorene (Spiro‐OMeTAD), which is costly, highly hygroscopic, and deliquescent, a respectable PCE of 15.14% is achieved with a promising device stability and negligible hysteresis.

Thermal and Structural Characterization of Methylammonium‐ and Formamidinium‐Halide Salts

“…Although there are many vapor deposition processes, most fall into one of two categories: single-step processes such as coevaporation, [7][8][9] and sequential, deposition-plus-reaction processes. [10][11][12][13] In coevaporation systems, it has proven difficult to control the flux of volatile organic reactants such as methylammonium iodide (MAI) using, for example, quartz crystal microbalance (QCM) technology. [11,[14][15][16] This is due to the high vapor pressure and low sticking coefficient of MAI, such that it does not obey line-of-sight mass transport nor does it deposit uniformly on the QCM surface.…”

Enhancing the operational stability of unencapsulated perovskite solar cells through Cu–Ag bilayer electrode incorporation

“…Organic-inorganic hybrid perovskites have demonstrated their potential in photovoltaic applications with power conversion efficiencies (PCE) steadily increasing, such that champion cells with a certied PCE of over 25% have been demonstrated. [1][2][3] Improvements in device PCE have been driven not only by modications to the composition [4][5][6] and processing 7,8 of the perovskite active layer but also by a number of complementary strategies, including surface defect passivation, [9][10][11][12] modication of the transport layers 13,14 and energy level alignment of interlayers. 14 However, the instability of perovskite solar cells (PSCs) remains one of the key barriers to further development, commercialization and ultimately wide-scale deployment.…”

Moth eye‐inspired highly efficient, robust, and neutral‐colored semitransparent perovskite solar cells for building‐integrated photovoltaics

“…Figure 4A shows the energy‐band diagram of the complete device. Band energy levels of SnO 2 , 45 spiro‐OMeTAD, 46 MoO 3 /IZO 47 are obtained from previously published literature. The VBM of Cs 0.05 FA 0.83 MA 0.125 PbBr x I 3‐x is 6.14 eV, derived by ultraviolet photoelectron spectroscopy (UPS) measurement (Figure S10), whereas the CBM is obtained by combining VBM with optical bandgap (Figure S8).…”