Surface Passivation of Triple-Cation Perovskite via Organic Halide-Saturated Antisolvent for Inverted Planar Solar Cells

Abstract

Cesium formadinium methylammonium triple-cation (CsFAMA) lead mixed-halide perovskites have been reported to promote unique photovoltaic properties with high efficiency and minimal hysteresis effects. Perovskite film quality is a vital parameter for improving the performance of perovskite solar cells (PSCs). Here, we report the growth of CsFAMA perovskites with microscale grains passivation grain boundaries by mixing HC­(NH2)2I (FAI) and CH3NH3Br (MABr) in isopropanol (IPA) as a post-treatment step to cause controlled Ostwald ripening, leading to secondary grain growth. Compared to the conventional preparation of perovskite films with a free organic halide antisolvent, this mixed-cation mixed-halide post-treatment created higher quality perovskite films in terms of morphology, electronic properties, energy level alignment, and carrier recombination, with the band gap adjusted at the optimal concentration. Treatment with the single cation and single halide presented by FAI and/or MABr in IPA treatment was also investigated, and the results showed that multiple band gap perovskite structures were obtained, which could be beneficial for band gap engineering. This method of perovskite preparation was tested in an inverted planar configuration with a hole transport layer (HTL) based on sulfonated poly­(thiophene-3-[2-(2-methoxy-ethoxy)­ethoxy]-2,5-diyl) (SP3MEET). The efficiency of the PSCs was dramatically boosted from 13.80% with the organic halide-free antisolvent to 17.62% when the mixed-cation mixed-halide approach was used. In addition, the PSCs treated with the mixed-cation mixed-halide solution exhibited excellent reproducibility, with a high fill factor and eliminated hysteresis. The CsFAMA photovoltaic device based on the single organic cation and single halide treatment approach showed power conversion efficiency of 15.82 and 15.90% for the FAI and MABr-treated films, respectively. Characterization of the S-P3MEET as HTLs found that good optoelectronic and morphological properties lead to improve the performance of the inverted PSC. However, with further research to align the energy levels at the S-P3MEET/perovskite interface, greater improvements in the PSCs are expected.

Materials and Methods for High‐Efficiency Perovskite Solar Modules

“…As antisolvents such as diethyl ether and chlorobenzene are highly toxic, it is not environmentally friendly. Although green antisolvents for scalable coating processes have been developed to address this problem using ethyl acetate (EA), [ 136 ] isopropanol (IPA), [ 137,138 ] and more, [ 109,110,135 ] these are economically disadvantageous because the antisolvent has to be continuously replenished to maintain the same conditions in different batches and ensure high reproducibility and reliability. Therefore, it is necessary to develop a technology for the formation of a high‐stability and ‐quality intermediate phase based on an adduct approach without an antisolvent.…”

Improved efficiency of inverted planar perovskite solar cells with an ultrahigh work function doped polymer as an alternative hole transport layer

“…In this process, mixed HC(NH 2 ) 2 I (FAI) and CH 3 NH 3 Br (MABr) in isopropyl alcohol with 4 mg ml À1 concentration was dropped onto the spinning substrate to enhance the Ostwald ripening of secondary grain growth of the perovskite films. [44][45][46][47][48] In this process, according to Fick's first law, the high gradient concentration will cause faster mass transportation between small grains (in treatment solution) and large grains (from precursor solution that is beginning film formation). 44 As a result, enough small grains in solution are re-deposited onto the large grains (de-nucleation of the larger grain) to enable the nucleation process to continue during spincoating, leading to larger grain sizes.…”

“…44 As a result, enough small grains in solution are re-deposited onto the large grains (de-nucleation of the larger grain) to enable the nucleation process to continue during spincoating, leading to larger grain sizes. [45][46][47][48] More details about the Cs 0.04 (FA 0 . 83 MA 0.17 ) 0.95 Pb(I 0 .…”

“…The stock solutions of the inorganic components (CsI, PbI 2 , and PbBr 2 ) were heated at 150 1C, which caused them to dissolve entirely, leading to a clear solution. This heating process lowers excess (PbI 1Àx Br x ) 2 accumulation on the perovskite film surface, 45 which would otherwise create poorer-quality perovskite active layers and, as a result, reduce PSC performance. 55,56 Additionally, the morphology of Cs 0.04 (FA 0 .…”

“…The energy level of electron transport layers and electrodes is taken from previous work, 49,62 while the energy of triple-cation perovskite valence-band maximum (VBM) and conduction-band maximum (CBM) are taken from Gelmetti et al 63 To grow the CsFAMA perovskites with large grains and novel passivation grain boundary onto the fluorinated S-P3MEET, saturated anti-solvent with organic halide was important for enhanced Ostwald Ripening. 45,64 All the HTL films' thickness was optimized to be 35 AE 1 nm, as estimated via AFM in tapping mode (Fig. S8, ESI †).…”