Pseudo‐Halide Perovskite Solar Cells

Abstract

class of solar absorber material. These halide perovskite materials have been known since 1970s, and their optical and electrical properties had been investigated by several groups. [1][2][3][4][5][6] Toward their application in solar cells, Kojima et al. first employed CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 as the light absorber using dye-sensitized solar cell configuration. [7] M. Grätzel and co-workers reported the first all-solid-state perovskite-based mesoscopic solar cells. [8] These class of perovskites material offers unique opto-electronic traits namely ambipolar charge transport, high absorption coefficient, and long electron/hole diffusion length, making them highly desired for PV application. Moreover, the ease of synthesis and low temperature crystallization makes them a good choice for low cost PV devices with high efficiencies. Being aware of these aforementioned remarkable optoelectronic properties and solution processability of halide perovskites, perovskite solar cells (PSCs) have attracted immense research attention worldwide. [9][10][11][12][13][14] They demonstrate a certified PCE of 25.5%, which is higher than that of organic solar cells and most of inorganic solar cells such as multi-crystalline silicon and copper indium gallium diselenide based solar cells. [15] In addition to their application in solar cells, owing to their intrinsic properties the halide perovskites have been employed in a wide range of optoelectronic devices, such as light-emitting diode (LED), lasers, photodetectors, and Perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) over 25%. Though their high PCE can be achieved by optimizing absorber layer and device interfaces, the intrinsic instability of perovskite materials is still a key issue to be resolved. Mixed-halide perovskites using multiple halogen constituents have been proved to improve robustness; however, the anion at the X site in the ABX 3 formula is not limited to halogens. Other negative monovalent ions with similar properties to halogens, such as pseudo-halogens, have the opportunity to form perovskites with ABX 3 stoichiometry. Recently, thiocyanates and formates have been utilized to synthesize stable perovskite materials. This review presents the evolution of pseudo-halide perovskite solar cells in the past few years. The intrinsic properties, their effects on crystal structure, and bandgap engineering of the pseudo-halide perovskites are summarized. Various thiocyanate compounds applied in the fabrication of perovskite solar cells are discussed. The fabrication process, film formation mechanism, and crystallinity of pseudo-halide perovskites are elucidated to understand their effects on the photovoltaic performance and device stability. Other applications of pseudo-halide perovskites are summarized in the final section. Lastly, this review concludes with suggestions and outlooks for further research directions.

Probing Lattice Dynamics in Two-Dimensional Inorganic Pseudohalide Perovskites with Ultrafast Infrared Spectroscopy

“…The resulting extremely short interlayer distances afford various unique properties among 2D pseudohalide perovskites, including low excitonic binding energy (E b ), decreased band gap (E g ), and large pressure response (piezochromism). 17,32,33 Studies of (MA) 2 Pb-(SCN) 2 I 2 thin films using 2D IR spectroscopy were performed previously. 34 The spectral diffusion, which measures structural fluctuations of the lattice variations that give rise to the inhomogeneously broadened CN stretch absorption band, was observed with a time constant of 4.1 ± 0.3 ps.…”

Homogeneous Grain Boundary Passivation in Wide‐Bandgap Perovskite Films Enables Fabrication of Monolithic Perovskite/Organic Tandem Solar Cells with over 21% Efficiency

“…Within 10 s annealing, plated‐like PbI 2 were appeared in the MA 1.06 PbI 2 Br(SCN) 0.12 film (Figure 4b), which should be caused by the interaction between the aggregated Pb(SCN) 2 and excessive MAI (Pb(SCN) 2 + 2MAI → PbI 2 + 2CH 3 NH 2 ↑ + 2HSCN↑) that induced the appearance of the aggregated plate‐like PbI 2 in the MA 1.06 PbI 2 Br(SCN) 0.12 film. [ 47,48 ] In contrast, the homogeneous elemental distribution in the MA 0.96 FA 0.1 PbI 2 Br(SCN) 0.12 film resulted in few PbI 2 rods (Figure 4g). Upon further annealing (20 s), more plated‐like PbI 2 were concentrated in the grain boundaries of the MA 1.06 PbI 2 Br(SCN) 0.12 film (Figure 4c), and almost all the grain boundaries of the film was saturated with PbI 2 after 30 s annealing (Figure 4d).…”

Recent advances in the interfacial engineering of organic–inorganic hybrid perovskite solar cells: a materials perspective

“…Therefore, this necessitates a more in-depth investigation of the interfaces between the device layers and the perovskite material itself during the device design and preparation, as well as optimization to obtain better interfacial properties for achieving devices with a higher photovoltaic performance. [25][26][27] As shown in Fig. 1a, since the photogenerated electron and hole carriers from the perovskite layer will transfer to the electrodes through the charge transport layers (CTLs), the perovskite/CTL and CTL/electrode interfaces are closely connected to the carrier dynamics (i.e., charge separation, transport, injection, collection and recombination) and significantly affect the device performance.…”