Controlling CH₃NH₃PbI_3–xCl_x Film Morphology with Two-Step Annealing Method for Efficient Hybrid Perovskite Solar Cells

Abstract

The methylammonium lead halide perovskite solar cells have become very attractive because they can be prepared with low-cost solution-processable technology and their power conversion efficiency have been increasing from 3.9% to 20% in recent years. However, the high performance of perovskite photovoltaic devices are dependent on the complicated process to prepare compact perovskite films with large grain size. Herein, a new method is developed to achieve excellent CH3NH3PbI3-xClx film with fine morphology and crystallization based on one step deposition and two-step annealing process. This method include the spin coating deposition of the perovskite films with the precursor solution of PbI2, PbCl2, and CH3NH3I at the molar ratio 1:1:4 in dimethylformamide (DMF) and the post two-step annealing (TSA). The first annealing is achieved by solvent-induced process in DMF to promote migration and interdiffusion of the solvent-assisted precursor ions and molecules and realize large size grain growth. The second annealing is conducted by thermal-induced process to further improve morphology and crystallization of films. The compact perovskite films are successfully prepared with grain size up to 1.1 μm according to SEM observation. The PL decay lifetime, and the optic energy gap for the film with two-step annealing are 460 ns and 1.575 eV, respectively, while they are 307 and 327 ns and 1.577 and 1.582 eV for the films annealed in one-step thermal and one-step solvent process. On the basis of the TSA process, the photovoltaic devices exhibit the best efficiency of 14% under AM 1.5G irradiation (100 mW·cm(-2)).

Effect of Annealing Process on CH3NH3PbI3-XClX Film Morphology of Planar Heterojunction Perovskite Solar Cells with Optimal Compact TiO2 Layer

“…Both two films exhibit the roughly same absorption edge at about 780 nm (corresponding to~1.55 eV optical bandgap of CH 3 NH 3 PbI 3-X Cl X ), which is consistent with the previous studies [35]. However, the absorption edge of MS film shows a slightly red shift, which should be due to the improved crystallinity with this method [36]. And this result is consistent with the conclusion from Figure 8.…”

Hybrid Perovskites: Effective Crystal Growth for Optoelectronic Applications

“…[4,6] In addition, total trap density of solvent annealed MAPbI3 is dramatically decreased down to the one-third of the thermal annealed counterpart (Figure 8d). The effect of solvent annealing is also verified with a mixed halide perovskite, MAPbI3-xClx by Liu et al [140] Combination of thermal annealing under nitrogen atmosphere followed by solvent annealing at 90 °C results in large crystal grains and reduces the overall resistance of solar cell device, resulting in a considerable device efficiency improvement.…”

A Study of Inverted-Type Perovskite Solar Cells with Various Composition Ratios of (FAPbI3)1−x(MAPbBr3)x

“…CH 3 NH 3 PbI 3− x Br x ( x = 0.1–0.15), as an absorbing layer, has been reported to improve the open voltage of photovoltaic devices [8]. CH 3 NH 3 PbI 3− x Cl x has been used to increase the exciton diffusion length to improve device performance [9,10,11,12]. HC(NH 2 ) 2 PbI 3 (FAPbI 3 ) [13,14,15,16] can reduce the optical bandgap (Eg ~1.48 eV), with an absorption edge of 840 nm, allowing photons to be absorbed over a broader solar spectrum.…”