Engineering the Hole Extraction Interface Enables Single‐Crystal MAPbI₃ Perovskite Solar Cells with Efficiency Exceeding 22% and Superior Indoor Response

Abstract

In polycrystalline thin films, the inherent grain boundaries that contain abundant charge traps can cause adverse effect on optoelectronic properties of perovskite materials, and defect passivation is necessary for efficient polycrystalline PSCs. [3] In contrast, perovskite single crystals offer an opportunity to further improve the efficiency of PSCs, due to the absence of grain boundaries as well as their orders of magnitude lower defect density and longer carrier diffusion length than those in their polycrystalline counterparts. [4] Recently, the efficiency of smallarea single-crystal PSCs based on 20 µm thick MAPbI 3 (MA = CH 3 NH 3 + ) absorber layer has reached 21.9% by using a low-temperature (<90 °C) inverse temperature crystallization (ITC) method. [5] Moreover, the near-infrared response of the devices can be expanded by incorporating FA (FA = CH(NH 2 ) 2 + ) into MAPbI 3 crystals, leading to a high PCE of up to 22.8%. [6] To construct large-area single-crystal PSCs, Liu et al. developed a refreshing-reiteration method to grow perovskite bulk single crystals with dimension as large as 120 mm. [7] Besides, they established a diamond-wire-sawing process to produce inchsized single-crystal perovskite wafers for fabrication of inchsized single-crystal PSCs. [8] For photovoltaic application, growth of micrometer-thick lead-iodide perovskite single crystals is necessary to promote carrier transport and collection. [9] Liu et al. designed an ultrathin geometry-defined dynamic-flow reaction system and realized the growth of large-area single-crystal perovskite wafers with controllable thickness, which provides a universal and effective strategy for application of perovskite single crystals in optoelectronic device design and fabrication. [10] In this method, a mass concentration of defects would unavoidably be generated at the interface due to the lattice mismatch between perovskite and hole transport layer (HTL). Huang et al. found that the trap density in perovskite single crystals increased by five orders of magnitude from interior to surface/interface, and most deep traps were detected near the HTL/perovskites interface. [11] On the other hand, the ion diffusion rate in the confined space is limited by the interaction between substrates and solvated Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V OC ) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb 2+ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transp...

Modulating preferred crystal orientation for efficient and stable perovskite solar cells—From progress to perspectives

“…And the improved ion diffusion contributes to the formation of high‐quality single crystals with reduced bulk defect density and higher carrier mobility. Consequently, they achieved a PCE of 22.1%, which is the highest value among the MAPbI 3 single‐crystal solar cell 167 17G).…”

“…Reproduced with permission. 166 Copyright 2020, American Chemical Society. (F) Schematic illustration of the interaction between perovskite single crystal and P3HT.…”

Perovskite Single‐Crystal Solar Cells: Advances and Challenges

“…[114] Stable γ-CsPbI 3 SCs at room temperature were demonstrated which, however, rapidly converted to δ-CsPbI 3 in humid environment. [115] An interfacial modification of the HTL/perovskite interface has been proved effective in order to reduce defect density, suppress nonradiative recombination, improve charge transport, and extraction, leading to MAPbI 3 single-crystal devices with 22.1% efficiency and long-term stability under air condition, maintaining 90% of the initial PCE after 1000 h. [116] Recently, stable CsPbBr 3 SCs where synthesized via a lowtemperature crystallization strategy in water. If compared to the CsPbBr 3 SCs grown with the inverse-temperature approach in DMSO, the newly developed material is characterized by a higher stability in ambient conditions and inhibited ion migration.…”

“…An interfacial modification of the HTL/perovskite interface has been proved effective in order to reduce defect density, suppress nonradiative recombination, improve charge transport, and extraction, leading to MAPbI 3 single‐crystal devices with 22.1% efficiency and long‐term stability under air condition, maintaining 90% of the initial PCE after 1000 h. [ 116 ]…”

Molecular design for perovskite solar cells

“…Various theoretical calculations have been performed to rationally understand the structure‐property relationships of the perovskite solar cell materials and the detailed charge carrier dynamics 16‐18 . Considering the fact that the perovskite‐related surfaces and interfaces are universally present in perovskite solar cells and dictate the device performance, the deep charge trap issues existing at the perovskite interfaces, 7,19‐22 and the carrier loss at the grain boundaries in the photoactive layer should be addressed. To this end, a number of surface and interface engineering methods have been employed to further improve the optoelectronic performance and stability of the perovskite solar cells 23,24 .…”