A Smooth CH₃NH₃PbI₃ Film via a New Approach for Forming the PbI₂ Nanostructure Together with Strategically High CH₃NH₃I Concentration for High Efficient Planar‐Heterojunction Solar Cells

Abstract

to 20.1% [ 2,3 ] within fi ve years. The theoretical limit of the PVSC effi ciency has been estimated to be 31%, which is very close to the Shockley-Queisser limit (33%). [ 4 ] Perovskite deposition is crucial to produce high-effi ciency PVSCs. Generally, there are mainly three methods, including onestep solution spin-coating, vacuum vapor deposition, and two-step sequential deposition to prepare the hybrid perovskite fi lm. [5][6][7][8][9][10][11][12][13] Two-step sequential deposition has recently been reported, [ 7 ] which provides an effi cient and low-cost route to high-performance PVSCs.In a typical two-step sequential deposition of perovskites such as MAPbI 3 (MA = CH 3 NH 3 + ), PbI 2 is fi rst deposited on the substrate (mesoporous or planar scaffold) by spin-coating or vacuum evaporation, subsequently transformed into the perovskite (MAPbI 3 ) by exposing it to an anhydrous isopropanol (IPA) solution of MAI. For the two-step sequential deposition, the conversion and fi lm morphology of the fi nal perovskite fi lm strongly depend on the initial PbI 2 fi lm during the fi rst step of the process. [ 7,14,15 ] Conventionally, PbI 2 from dimethyl formamide (DMF) solution tends to form a layered and dense crystalline fi lm on a fl at substrate. However, the complete conversion of PbI 2 to perovskite on exposure to the MAI solution usually requires several hours. [ 7 ] However, this long reaction time in MAI solution could lead to the dissolution of perovskite fi lms. These drawbacks make it diffi cult to fabricate planar-structured PVSCs by sequential deposition method.Several strategies have been developed to solve this problem, including using elevated reaction temperature, [ 16,17 ] controlling the crystallization of PbI 2 by employing strong coordinative solvent of dimethyl sulfoxide [ 14 ] or using MAI vapor instead of MAI solution. [ 18 ] Recently, a cloudy PbI 2 fi lm prepared by gas-quenching treatment has been reported by Vak and co-workers, [ 19 ] which also enhances the conversion of PbI 2 to perovskites in the process of roll-to-roll fabrication. Zhao & Zhu [ 14 ] developed a new three-step sequential deposition process, where a unstable PbI 2 ·CH 3 NH 3 Cl precursor fi lm is fi rst deposited on the mesoporous TiO 2 substrate and followed by thermal decomposition to form PbI 2 fi lm; the PbI 2 fi lm The photovoltaic performance of perovskite solar cells (PVSCs) is extremely dependent on the morphology and crystallization of the perovskite fi lm, which is affected by the deposition method. In this work, a new approach is demonstrated for forming the PbI 2 nanostructure and the use of high CH 3 NH 3 I concentration which are adopted to form high-quality (smooth and PbI 2 residue-free) perovskite fi lm with better photovoltaic performances. On the one hand, self-assembled porous PbI 2 is formed by incorporating small amount of rationally chosen additives into the PbI 2 precursor solutions, which signifi cantly facilitate the conversion of perovskite without any PbI 2 residue. On the other hand, by...

Controlled crystallization of CH3NH3PbI3 films for perovskite solar cells by various PbI2(X) complexes

“…[44,[48][49][50] Thus we investigated the surface and cross-sectional morphology of the perovskite films fabricated from various PbI 2 (X) complexes by scanning electron microscopy (SEM) as shown in Fig. 4.…”

Monitoring Thermal Annealing of Perovskite Solar Cells with In Situ Photoluminescence

“…[16,17] Other recipes that yield efficiencies exceeding 13% use different solvents, [18] nonsolvent washing, [19,20] alkyl halide additives, [21] acid additives, [22,23] hot casting, [23,24] and multistep processing routes. [3,25,26] The development of such a multitude of procedures is, at least in part, a consequence of the fact that it is not straightforward to reproduce the highest efficiency cells among different research groups. Whether this relates to differences in material sources and equipment, or to a lack of experience, is presently unknown.…”

Additive-Assisted Controllable Growth of Perovskites

“…This additive idea has later been adapted by other groups using a small amount of tBP or even H 2 O as a good additive to form some PbI 2 x[additive]. 29,30 These additives can also smooth the precursor films and help obtain high-quality perovskite thin films. Figure 12 shows an example using H 2 O as the additive to control the perovskite film morphology.…”