Interface Modification by Simple Organic Salts Improves Performance of Planar Perovskite Solar Cells

Abstract

significantly improve the performance of MAPbBr 3 cells, [20] this is not the case for CsPbBr 3 -based devices. [21] It is important to note that all reports on devices without HTM are for cells with the perovskite in/on mp scaffolds, and not in a flat (planar) cell configuration, that is, with the perovskite directly on dense TiO 2 . In principle, provided the perovskites transfer charges efficiently, modification of their interface may facilitate directional charge transfer and enhance device performance, analogous to surface modifications in common semiconductor devices [22] or conductors. [23] Here we show that a simple organic salt, tetrabutylammonium hexafluorophosphate (TBAPF 6 ), deposited with small amounts of polymethyl methacrylate (PMMA), affords planar methylammonium lead bromide (MAPbBr 3 (Cl)) devices (fabricated on dense TiO 2 ) having 4.4% efficiency and V OC = 1.24 V, a significant improvement in comparison with similar planar devices but without the modified interface (0.64% efficiency, V OC = 0.82 V). Our findings suggest that tuning interfacial properties with simple polar compounds may represent an advantageous approach to improving perovskite solar cell efficiency. Thus, planar devices without conventional hole conductors may present a cost-efficient alternative to currently employed architectures.We used readily available tetrabutylammonium salts (TBAX, X = halide, BF 4 , or PF 6 ) to modify the interfacial properties. The salts possess high dielectric constant and good charge transporting characteristics, [24] and have very good solubility in various organic solvents. TBAX salts (TBABr, TBAI, TBABF 4 , and TBAPF 6 ) were spin-coated on MAPbBr 3 (Cl) perovskite layers at room temperature. When we deposited the TBABr and TBAI, the perovskite film was etched (more so with TBABr, Figure S1, Supporting Information), whereas the films are stable upon deposition of TBAPF 6 ( Figure S1, Supporting Information). Optical transmission spectroscopy and X-ray diffraction (XRD) of perovskite/TBAPF 6 (and also of perovskite/TBABF 4 ) films on glass substrates ( Figure S2, Supporting Information) show that the perovskite structure and absorption spectrum are not changed.The devices were fabricated as follows. The CH 3 NH 3 PbBr 3 (Cl) perovskite film was deposited by spincoating the solution of PbCl 2 and CH 3 NH 3 Br in a 1:3 ratio on the dense TiO 2 (d-TiO 2 ) coated FTO substrate (planar cell architecture), and subsequently annealed (chloride was not detected in the film but its traces can be present). [25] Then TBAPF 6 was deposited on the perovskite layer from solutions of different concentrations, and coated with gold. The corresponding FTO/d-TiO 2 /MAPbBr 3 (Cl)/TBAPF 6 /Au solar cell characteristics are given in Figure S3 and Table S1 (Supporting Information) Perovskite solar cells have recently become a focus of interest because of their high efficiency that is achieved using lowcost constituents and fabrication via solution processing techniques. [1][2][3][4][5][6] Commonly used perovskites are...

One‐step Solution‐Processed Formamidinium Lead Tribromide Formation for Better Reproducible Planar Perovskite Solar Cells

“…In recent years, high‐voltage perovskite solar cells using the bromide analogue of methylammonium lead iodide (MAPbI 3 ) with high band gap and high V oc have drawn reasonable attention. Among hybrid perovskites, methylammonium lead bromide (MAPbBr 3 ) and formamidinium lead bromide (FAPbBr 3 ) with band gaps of 2.31 and 2.26 eV, respectively, are particularly interesting in this respect as their material compositions are near‐ideal for producing a high photovoltage. However, FAPbBr 3 was used less compared to MAPbBr 3 .…”

“…Be it photoelectrochemical applications or top cells in tandem-architecture solar cells,i tis always challenging to fabricatet ailored high-open-circuit-voltage( V oc )s ingle-junction solar cells.F or example,t oo btain H 2 by water splitting, as olar fuel cell requires more than 1.23 V. [7] In recent years, high-voltage perovskite solar cells using the bromide analogue of methylammonium lead iodide (MAPbI 3 )w ith high band gap and high V oc have drawn reasonable attention. Amongh ybrid perovskites,m ethylammonium lead bromide (MAPbBr 3 ) [8][9][10][11][12][13][14] and formamidinium lead bromide (FAPbBr 3 ) [15,16] with band gaps of 2.31 and 2.26 eV,r espectively,a re particularly interesting in this respecta st heir material compositions are near-ideal for producing ah igh photovoltage.H owever, FAPbBr 3 was used less compared to MAPbBr 3 .I nf act, thus far only few studies reported the successful use of pure FAPbBr 3 as light absorber in hybridp er-ovskite solar cells. [15][16][17] Hanusche tal.…”

Theoretical Device Engineering for High‐Performance Perovskite Solar Cells Using CuSCN as Hole Transport Material Boost the Efficiency Above 25%

“…There are interface defects, usually represented by defect density, which affect the transport of photo induced charge carriers across the interface due to lattice mismatch, poor coordination of electrons and holes, and dislocations at the interfaces. This can be controlled by controlling charge losses and adopting some suitable film deposition methods like atomic layer deposition, chemical vapor deposition, metalorganic chemical vapor deposition, and molecular beam epitaxy . A theoretical guide is very critical to experimental modification of the interfaces in PSCs .…”

Impact of Dipole Effect on Perovskite Solar Cells

“…For example, using organic amine salts to passivate the surface of perovskite films can form interface dipoles and alter the effective W F . [90] Nevertheless, the use of naphthalimide-based organic small molecules can passivate the perovskite surface and generate interfacial electric dipoles to effectively inhibit carrier recombination (Figure 7a). [91] The same dipolar materials also affect the properties of perovskite films in different ways.…”