Structural and Electronic Studies on the All-Inorganic CsPb(I_1-xBr_x)₃ Perovskite in Terms of Light Soaking, Interfacial Layers and Crystallization Kinetics for Efficient and Stable Solar Cells

When and Where

Apr 12, 2023
5:00pm - 7:00pm

Moscone West, Level 1, Exhibit Hall

Presenter

Xiao Wu

Xinhui Lu

Co-Author(s)

Xiao Wu¹,Xinhui Lu¹

The Chinese University of Hong Kong¹

Abstract

Xiao Wu¹,Xinhui Lu¹

The Chinese University of Hong Kong¹

Organic-inorganic hybrid perovskites have shown promising applications in optoelectronic devices. However, the volatile nature of organic cations such as methylammonium (MA+) and formamidinium (FA+), imposes intrinsic thermal stability issues. To this concern, inorganic CsPbX3 (X=I- or Br-) perovskites have attracted rising interest in recent years, owing to their excellent thermal stability and suitable bandgap for tandem applications with narrow-bandgap solar cells such as crystal silicon and CIGS. However, on one hand, the efficiencies of inorganic perovskite solar cells (PSCs) are still lagging behind the hybrid counterparts, demanding fundamental studies on the crystallization mechanisms for high-quality films and the interfacial modifications for efficient charge collection. On the other hand, operational stability under light illumination has always been a concern for solar cells, especially for the halide perovskites with easily mobile halide ions. Here, we will first present a remarkable light soaking (LS) induced performance enhancement of CsPb(I1-xBrx)3 PSCs.[1] We clarified the impact of light and radiative heating on the crystal structure via in situ grazing-incidence wide-angle X-ray scattering measurements (GIWAXS) and elucidated the common LS phenomenon in CsPb(I1-xBrx)3 with various Br/I ratio, which is related to ion migration. Also, we proposed an effective means to suppress the LS effect for obtaining more stable and efficient CsPb(I1-xBrx)3 PSCs. Second, we report an efficient low-temperature processed ZnO electron transporting layer engineered by incorporating PbX2 (X=I-, Cl- and CH3COO-).[2] This method could tune the oxygen vacancies in ZnO, promote the growth of the perovskite layer with improved morphology and orientational order, and form a favorable energy level alignment with the perovskite layer, thus facilitating charge extraction and suppressing charge recombination. Finally, we elucidate the phase transition mechanism of inorganic CsPb(I1-xBrx)3 from precursor state to perovskite film via GIWAXS measurement and DFT calculations. It was discovered the phase transition was not a simple conversion from the room-temperature stabilized yellow δ-phase to the high-temperature stabilized black phase. Instead, a multistage phase transition of the γ-δ-γ regime was found throughout the annealing process, resulting in poor film quality. To address this issue, we proposed a method to suppress the transition to δ-phase during heating and achieved efficient (20.1%) and stable CsPb(I1-xBrx)3 solar cells. Reference: (1) Wu, X.; Ma, J.; Qin, M.; Guo, X.; Li, Y.; Qin, Z.; Xu, J.; Lu, X. Control over Light Soaking Effect in All-Inorganic Perovskite Solar Cells. Adv. Funct. Mater. 2021, 2101287. (2) Wu, X.; Zhang, J. Q.; Qin, M. C.; Liu, K.; Lv, Z.; Qin, Z. T.; Guo, X. L.; Li, Y. H.; Xu, J. B.; Li, G.; et al. ZnO electron transporting layer engineering realized over 20% efficiency and over 1.28 V open-circuit voltage in all-inorganic perovskite solar cells. Ecomat 2022, 4 (4). DOI: 10.1002/eom2.12192.