Halide Diffusion Equilibrium and Its Impact on Efficiency Evolution of Perovskite Solar Cells

Abstract

Understanding the degradation mechanism of perovskite solar cells (PSCs) is of particular importance to solve their instability issue, which is one of the major hindrances toward commercialization. Here, it is shown that a halide diffusion equilibrium exists at the heterointerface of perovskite devices, which strongly impacts the evolution of device performance. The combined experimental and theoretical studies reveal that halide components diffuse from perovskite to fullerene layers in a p‐i‐n PSC device and equilibrate with an iodine density of 1018–1019 cm−3 within 80 h under dark aging condition. It is found that there is a strong correction between the device efficiency and halide diffusion equilibrium of PSCs, as the diffused halides can chemically dope the transport layer and result in the nonstoichiometric perovskite surface, leading to both initial enhancement and long‐term loss of the photovoltaic efficiency of solar cells. In response to this issue, a predoping strategy is developed to attain the halide diffusion equilibrium once the device is fabricated, thereby avoiding the further halide migration and initial efficiency variations. As a result, the as‐prepared PSC achieved an efficiency of 23.13% as well as stable power output under continuous one sun illumination.

Mitigating Surface Deficiencies of Perovskite Single Crystals Enables Efficient Solar Cells with Enhanced Moisture and Reverse‐Bias Stability

“…Besides, high surface trap density provides large amounts of channels for ion migration, which can cause undesired hysteresis and accelerate reverse-biasinduced device degradation. [24,25] Nevertheless, in comparison to well-established surface passivation strategies in perovskite polycrystalline films, [26][27][28] passivating surface of perovskite single crystals are rarely reported. [29][30][31] In addition to high trap density, the surface of perovskite single crystals is moisture sensitive.…”

Tetrabutylammonium Bromide Functionalized Ti3C2Tx MXene as Versatile Cathode Buffer Layer for Efficient and Stable Inverted Perovskite Solar Cells

“…This result demonstrates that the TBAB-Ti 3 C 2 T x CBL can remarkably improve interface contact quality and passivate electronic defects. [38,39,43] We verified that p-Ti 3 C 2 T x CBL can improve electrical conductivity and passivate PCBM/Ag interfacial defects, thereby increasing charge transport and reducing charge recombination. Moreover, the TBAB-Ti 3 C 2 T x CBL with higher electrical conductivity enables optimization of energy level structure and effective inhibition of iodine ions migration from perovskite layer to Ag cathode, thus realizing efficient carrier transport for higher photovoltaic performance.…”

“…Compared with the p-Ti 3 C 2 T x based device, the TBAB-Ti 3 C 2 T x based device exhibits the lower HI, which may be originated from the higher electrical conductivity and better matched energy level alignment as well as the effective inhibition of iodine ions migration from perovskite layer to Ag cathode. [38,39] Time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profile measurements are conducted to investigate the elemental distribution throughout the devices, and the highest intensity of characteristic ion counts is used to determine the functional layers of the devices. As shown in Figure 6a, the control device possesses much accumulation of iodine ions at the PCBM/Ag interface, which is attributed to the strong interaction between the Ag electrode and the iodine ions migrated from perovskite layer.…”

Low‐Temperature Synthesis of SnO2 Nanocrystals as Electron Transport Layers for High‐Efficiency CsPbI2Br Perovskite Solar Cells

“…[25][26][27][28] Intensive researches were done in grain morphology and surface defect passivation of perovskite thin films. [29][30][31][32][33][34] On the other hand, energy loss at the interface or transport layers cannot be neglected. [35] For a long period, TiO 2 is the most widely used electron transport layer (ETL) material, but its low charge conductivity and high-temperature process are adverse to acquiring efficient and stable PSCs.…”