Organometal Halide Perovskite Solar Cells with Improved Thermal Stability via Grain Boundary Passivation Using a Molecular Additive

Abstract

Organometal halide perovskite solar cells (PeSCs) are regarded as promising photovoltaics due to their outstanding power conversion efficiencies (PCEs). However, even though their PCEs are achieved over 20%, their intrinsically poor stability is a big bottleneck for their practical uses. Here, a simple method is reported using phenyl‐C61‐butyric acid methyl ester as a molecular additive to improve thermal stability of organometal halide perovskite crystals, which also improves the PCEs of the associated PeSCs. Moreover, by varying the grain size of perovskite crystals up to ≈150 µm, it is demonstrated that grain boundary plays a significant role in their thermal stability. Cells with smaller grain interface area (i.e., larger grain size) have higher thermal stability. The additive is located at grain boundaries and found to induce electron transfer reactions with halogens in the perovskite. The reaction products chemically passivate perovskite crystals and strongly bind halogen atoms at grain boundaries to their crystal lattice, preventing them from exiting from the crystal lattice, which improves thermal stability of perovskite crystals. This study offers a simple method for improving thermal stability of perovskite without any loss and opens up the possibility of the use of various molecular additives to achieve highly stable PeSCs.

Carrier Interfacial Engineering by Bismuth Modification for Efficient and Thermoresistant Perovskite Solar Cells

“…The slope (slope = −E a /k B ) is related to the activation energy E a . [58] As illustrated in Figure 4b for MB 1.5 modified films, enlarging grains size and decreasing grain boundaries from which the by-products (HI, CH 3 NH 2 , etc.) [52,57] According to the data shown in Table S6 (Supporting Information), the activation energy is determined to be 300.3 meV for the control film.…”

“…[52,57] According to the data shown in Table S6 (Supporting Information), the activation energy is determined to be 300.3 meV for the control film. [58,60,61] Third, 2D flake-like crystals can be observed in 3D perovskite structure through the SEM in Figure 4c. The enhanced activation energy suggests that the Bi 3+ modification in perovskite films could effectively reduce the structural defects, and increase the activation energy, and resulting in better thermal stability.…”

Retarding Thermal Degradation in Hybrid Perovskites by Ionic Liquid Additives

“…For example, the incorporation of specific small molecules can retard crystal growth, modulate the crystal orientation, and suppress surface defects . In addition, several p‐type or n‐type semiconductors have been also tested as additives, leading to a bulk‐heterojunction like distribution which passivates trap states and provides more efficient intergrain carrier transport . Also, small molecules like ionic liquids (ILs) have other conducive properties that can be beneficial to the pristine material, including good conductivity, low vapor pressure, and high thermal stability …”

“…In the last few years, several investigations have focused on the use of additives to modulate the perovskite properties and suppress degradation pathways . However, improved stability is often related to the increased moisture resistance under humid environments, similarly to employing an extra “blocking layer” to protect the film from moisture.…”

“…However, improved stability is often related to the increased moisture resistance under humid environments, similarly to employing an extra “blocking layer” to protect the film from moisture. To the best of our knowledge, there are no investigations that specifically target the thermal stability of the material, and studies that mention thermal stabilization either do not report stability tests or, if reported, the tests are often performed under arbitrary conditions, i.e., devices stored under dark conditions, without continuous light illumination, bias or at undefined (or low, ≈25 °C) temperatures, and even include very poor performance or extremely short testing times (≤50 h) . As a consequence, a comparison among the different strategies becomes extremely challenging.…”