Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%

Abstract

TiO 2 /FTO, the cross sectional scanning electron microscopy (SEM) image of which is shown in Fig. 1a. Employing this solar cell configuration, we achieve the best PCE of 21.6% with a PMMA concentration C PMMA =0.6mg/ml. The photovoltaic metrics of the device are as follows: short-circuit current density (J SC ) = 23.7 mA cm -2 , open circuit voltage (V OC ) = 1.14 V, and a fill factor (FF) = 0.78 (Fig. 1b). One of the devices was sent for certification to Newport Corporation PV Lab, an accredited PV testing laboratory, confirming a PCE of 21.02% (supplementary Fig.1 Fig. 3, Tab. 2a and 2b). The photovoltaic metrics of the PSCs fabricated from PTNG method varying C PMMA are summarized in Fig. 1c.Upon increasing the PMMA concentrations (C PMMA , mg/ml) in mixed chlorobenzene and toluene (volume ratio of cholorobenzene and toluene is 9:1) solution, the PCE first augments and subsequently decreases with a peak at C PMMA = 0.6. Upon increasing the C PMMA from 0 to 0.6 mg/ml, the V oc rises from 1.10V to 1.14 V, and the FF from 0.74 to 0.78. To further examine the crystal structure, we conducted thin layer X-ray diffraction (XRD) measurements for perovskite films deposited on m-TiO 2 /blTiO 2 /FTO substrates (Fig.3a). The peak at 12.5 o arises from the (001) lattice planes of hexagonal (2H polytype) PbI 2. The excess PbI 2 is believed to passivate surface defects, increasing the solar cell performance 13 . All the samples show the same trigonal perovskite phase with the dominant (111) lattice reflection. We speculate the (111) plane to exhibit the smallest surface energy because the majority of grains exhibit this orientation to minimize the total Gibbs free energy of the system. With increasing C PMMA , the (111) oriented grains grew faster by consuming neighboring non-oriented crystals, either by regular grain growth or grain attachment, as evidenced by the increased ratio between the (111) and (123) peak at 13.9 ° and 31.5° in the presence of PMMA. By taking the full width at half maximum (FWHM) of the (111) reflection, we calculate the crystallite size using Scherrer's equation. Their dimension increases from 41 to 55, 70, 94, and 112 nm by increasing C PMMA from 0 to 4mg/ml.We attribute the larger crystal sizes to the templating effect of PMMA on the crystal The X-ray photoelectron spectroscopy (XPS) in Fig. 3d shows Pb 4f spectra.There are two main peaks Pb 4f7/2 and Pb 4f5/2 at 138 and 142.8 eV, respectively.We attribute the two small peaks located at 136.4 and 141.3 eV to the presence of In conclusion, we introduce a new method for preparing high-electronic quality perovskite films and implement it for the fabrication of PSC with excellent performance their certified PCE attaining 21 %. Further development of the method will enable further performance gains. Acknowledgement:

Crystallization Kinetics and Morphology Control of Formamidinium–Cesium Mixed‐Cation Lead Mixed‐Halide Perovskite via Tunability of the Colloidal Precursor Solution

“…It has been reported that the measured DLS intensity relates to rod-shaped colloids. [25] As we show in Figure S2 (Supporting Information), we observe the presence of these nanorods in unheated thin films prepared with an acid-free solution, consistent with observations made by Yan et al and Bi et al [25,33] Perovskite films fabricated from a solution with a high concentration of colloids quickly turn dark in the process of spin-coating, while film spun with "colloid-free" solutions remained yellow. Notably, we observe similar time-dependence behavior for "cesium-free" FAPb(Br 0.2 I 0.8 ) 3 and "formamidinium-free" CsPb(Br 0.2 I 0.8 ) 3 precursor solutions, suggesting that the colloids are lead polyhalide colloids ( Figure S3, Supporting Information).…”

Fabrication and characterization of perovskite solar cells added with MnCl2, YCl3 or poly(methyl methacrylate)

“…For the preparation PMMA solutions, PMMA(Sumitomo Chemical) solution with different concentrations from the mixed solvent of chlorobenzene (Wako Pure Chemical Industries) and toluene(Wako Pure Chemical Industries) (volume ratio of chlorobenzene and toluene is 9:1 ) was pipetted onto the perovskite layer by spin-coating at 4000 rpm for 30 s and annealed at 100 °C for 15 min [18]. Then, a hole transport layer (HTL) was prepared by spincoating at 4000 rpm for 30 s. As the HTL, a solution of 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD, Sigma Aldrich, 36.1 mg) in chlorobenzene (Wako Pure Chemical Industries, 0.5 mL) was mixed with a solution of lithium bis (trifluoromethylsulfonyl) imide (Li-TFSI, Tokyo Chemical Industry, 260 mg) in acetonitrile (Sigma Aldrich, 0.5 mL) for 24 h. The former solution with 4-tertbutylpyridine (Sigma Aldrich, 14.4 μL) was mixed with the Li-TFSI solution (8.8 μL) for 30 min at 70 °C.…”

Towards large-area perovskite solar cells: the influence of compact and mesoporous TiO2 electron transport layers

“…In the recent years, the power conversion efficiency (PCE) of PSCs have rapidly climbed from 3.8% to 22.7% [6][7][8][9][10][11][12][13][14][15][16]. Much effort has been focused on improving the crystallographic quality [12,17] and adjusting the composition of the perovskite layer [18][19][20] to improve the PCE and stability. As an essential part, the electron transport layer (ETL) also plays a crucial role in device performance.…”