Enhancing Charge Carrier Transport in the Carbon-Electrode-Based CsPbI₂Br Perovskite Solar Cells via I/Br Homogenization Process Modulation and Oleic Acid Surface Passivation

Abstract

The carbon-electrode-based CsPbI2Br perovskite solar cells (C-PSCs) are promising photovoltaic technology because of their enhanced stability and low cost. However, the CsPbI2Br film suffers from uneven surface morphology with stripes and the defect-rich surface, which are detrimental to the charge carrier transport between perovskite and carbon. Here, we demonstrate that the formation of stripes is directly related to the I/Br homogenization process during annealing. By introducing a pre-annealing treatment before high temperature annealing, the I/Br homogenization process is modulated and the stripe is successfully wiped off. Besides, enhanced charge carrier transport in the C-PSCs is achieved. Oleic acid (OA) is then introduced to modify the stripe-free perovskite film surface. It is revealed that the carboxyl group in the OA molecule can passivate the undercoordinated Pb ions, leading to further improved charge carrier transport. Eventually, a power conversion efficiency (PCE) of 15.57% is achieved, which is among the highest PCE for the CsPbX3-based C-PSCs. This work demonstrates that combining surface planarization with surface passivation is an effective strategy for developing highly efficient C-PSCs.

Multi‐Site Intermolecular Interaction for In Situ Formation of Vertically Orientated 2D Passivation Layer in Highly Efficient Perovskite Solar Cells

“…Moreover, as has been reported, inhomogeneity of ions in the perovskite crystals could cause shoulder peaks in XRD pattern. [42,43] The shoulder peaks at 2𝜃 of 8.8°and 10.7°disappear when the temperature raises to 130 °C, indicating a suppressed phase segregation and ordered distribution of ions in the crystal structures. As shown in Figure S3 (Supporting Information), we compared the XRD patterns of the fresh and aged films of (PA) 2 PbI 2 Cl 2 and no obvious change was detected, which further confirmed the good stability of (PA) 2 PbI 2 Cl 2 .…”

Interfacial Treatment by 1,4-Phenyldiammonium Diiodide to Significantly Improve the Performance of Carbon-Based CsPbI2Br Solar Cells

“…6,7 Especially, the absence of the HTMs normally leads to a high defect density at the perovskite/carbon interface, which is not conducive to hole extraction. 8 Therefore, the PCE of HTMfree carbon-based PSCs, just beyond 15% to date, 9 is generally lower than that of the metal electrode-based PSCs. 10,11 Interface engineering is one of the viable approaches to optimizing the energy level arrangement and meanwhile to passivating defects for various devices, which has also been applied in the study of the HTM-free carbon-based PSCs.…”

“…However, although HTM-free carbon-based CsPbI 2 Br PSCs have these advantages, there are also some critical issues needing to be well addressed, such as poor interfacial contact and energy level mismatch between CsPbI 2 Br and carbon materials, which severely restrict improvement of the photovoltaic performance. , Especially, the absence of the HTMs normally leads to a high defect density at the perovskite/carbon interface, which is not conducive to hole extraction . Therefore, the PCE of HTM-free carbon-based PSCs, just beyond 15% to date, is generally lower than that of the metal electrode-based PSCs. , …”

Enhanced comprehensive performance of carbon-based hole-transport-layer-free CsPbI2Br solar cells by a low-cost and stable long chain polymer

“…25 However, the device performance including PCE (to date, the best PCE is only 15.57%, far lower than that of other CsPbI 2 Br solar cells) and operation stability is limited by the poor crystallinity of CsPbI 2 Br, and the mismatched energy levels and poor contact between the carbon electrode and the perovskite layer. 26–29 Therefore, improving the crystallinity of CsPbI 2 Br and the contact between the carbon electrode and the perovskite layer is important to realize a high-performance HTL-free carbon-based solar cell. For various strategies of addressing these concerns, additive engineering is a viable approach and meanwhile has attracted extensive attention.…”