Tuning the Surface Energy of Hole Transport Layers Based on Carbazole Self‐Assembled Monolayers for Highly Efficient Sn/Pb Perovskite Solar Cells

Abstract

Recently, carbazole‐based self‐assembled monolayers (SAMs) have been utilized as hole transport layers (HTLs) in perovskite solar cells. However, their application in Sn or mixed Sn/Pb perovskite solar cells has been hindered by the poor wettability of the perovskite precursor solution on the carbazole surface. Here a self‐assembled bilayer (SAB) comprising a covalent monolayer (Br‐2PACz) and a noncovalent wetting layer (4CzNH3I) as the HTL in a Cs0.25FA0.75Sn0.5Pb0.5I3 perovskite solar cell is proposed. It is demonstrated that the wetting layer completely solves the problem due to the higher polarity of the surface and, furthermore, the ammonium groups help in the passivation of trap states at the buried SAB/perovskite interface. The introduction of the SAB enhances the device reproducibility with an average efficiency of 18.98 ± 0.28% (19.45% for the best device), compared to 11.54 ± 9.36% (19.34% for the best device) for the SAM‐only devices. Furthermore, the improved perovskite processability on the SAB helps to increase the reproducibility of larger size device, where, a 12.5% efficiency for a 0.8 cm2 active area device compared to 0.68% for the best SAM‐based solar cell is demonstrated. Finally, the device's operational stability is also improved to 358 hours (T80%), compared to 220 hours for the SAM‐based solar cell.

Reducing Nonradiative Losses of Air‐Processed Perovskite Films via Interface Modification for Bright and Efficient Light Emitting Diodes

“…Correspondingly, we observe that the peak value of P 2p signal in Figure S4d-g (Supporting Information) decreases as the X-ray incidence angle increases, which is similar with the 2PACz processed in inert atmosphere. [21][22][23] Such alignment of 2PACz molecules would lead to the exposure of hydrophobic carbazole groups in 2PACz to the humid air. In this case, the 2PACz molecules are expected to rearrange themselves to reduce the contact between the hy-drophobic groups with the moisture in the ambient air, which could cause the aggregation of 2PACz molecules, as schematically presented in Figure 1a.…”

Facile Posttreatment of Self‐Assembled Monolayers for Efficient Inverted Perovskite Solar Cells

“…[7,8] In this regard, research has been devoted to surface treatment and molecular designs, so as to tune the work function and charge extraction of the device. [9][10][11] For instance, previous works have reported a superwetting SAM that improves the film formation of SAM and perovskite, minimizing defect states at the buried interface of PSCs. [2] Solvents such as ethanol were applied to obtain monolayer by removing loosely bound SAM molecules on the surface, which is beneficial to reducing the series resistance.…”

Connecting Interfacial Mechanical Adhesion, Efficiency, and Operational Stability in High Performance Inverted Perovskite Solar Cells

“…9,10 Most recently, a bilayer approach has also been used, where an additional molecular "wetting" layer is introduced above the SAM. 21,22 However, the important issue of how carbazole-based SAMs affect the mechanical adhesion of buried ITO/MHP interface has not been addressed.…”

“…(Br-2PACz SAM has been used in PSCs recently, but the interfacial mechanical properties were not evaluated in those studies. 14,22 ) This use of I-2PACz SAM in place of 2PACz SAM makes the ITO surface more polar and polarizable for better wettability. Also, the iodine termination provides a favorable dipole.…”