SnO₂ Passivation and Enhanced Perovskite Charge Extraction with a Benzylamine Hydrochloric Interlayer

Abstract

Perovskite solar cells (PSCs) have gained much attention because of their expressive power conversion efficiency (PCE) of up to 25.5%. A good contact and a well-aligned energy level at the buried interfaces between electron transport layers (ETLs) and perovskite films play an essential role in promoting charge-carrier collection and suppressing nonradiative recombination. Currently, low-temperature-processed SnO2 thin films are widely used as the ETLs to achieve efficient and stable planar PSCs. However, fabricating proper SnO2/perovskite interfaces with a good contact and a well-aligned energy level is necessary but implies a great challenge. Herein, we modify the SnO2 ETL using benzylamine hydrochloride (BH), which is expected to facilitate the energy level alignment and to enhance perovskite crystallization. Moreover, the BH interlayer is found to effectively reduce the trap-state density and thereby improve the charge-carrier extraction between the ETL and the perovskite layer. Consequently, the PSC with BH modification yields a higher PCE, a lower hysteresis, and better stability than the device without a BH interlayer. This study highlights the key role of molecule modification of ETLs in designing efficient and stable PSCs.

Deciphering the Morphology Change and Performance Enhancement for Perovskite Solar Cells Induced by Surface Modification

“…[33] The PL spectra in Figure 3F show that the control sample has a peak position of 783 nm, agreeing well with the value reported in literature. [30,35] The peak position is 776 nm for the BTACl-modified film, showing a slight blue shift compared to the control sample, which is consistent with the UV-Vis result. This observation is due to the formation of 2D perovskites after BTACl treatment, which gives a larger bandgap than 3D MAPbI 3 .…”

“…This observation is in line with our previous work. [ 20 , 35 ] However, the temporal evolution of XRD characteristics differs. Regardless of relative humidity, the peak intensities of (110) plane decrease over time in the control film, whereas they remain almost unchanged in the BTACl‐treated sample.…”

Stability and efficiency improvement of perovskite solar cells by surface hydroxyl defect passivation of SnO2 layer with 4-fluorothiophenol

“…X-ray diffraction (XRD) data show little change in crystal structure of the perovskite film before and after surface modification of SnO 2 (Fig. 3(c)), which might be related to the surface roughness 22 being unaffected by the passivation (Table S3†). In addition, absorption onset and absorbance of the perovskite films are also unaffected by the surface modification (Fig.…”

“…Thus, it is necessary to passivate the surface defects of solution-processed SnO 2 in order to reduce the trap state between SnO 2 and perovskite layer. Ionic salts such as KCl, 8,15 KF, 16 and NH 4 F, 14 functional organic compounds like zwitterions, 17 self-assembled monolayers, 18–20 2-methylbenzimidazole, 21 benzylamine hydrochloride, 22 and phosphate 23 were proposed as chemicals for passivating the surface of SnO 2 . For instance, NH 4 F treatment modified surface hydroxyl groups by inducing Sn–F chemical bonding via capturing the surface hydroxyl anions by NH 4+ , 14 and for the case of zwitterions, 17 anions were anchored on the SnO 2 surface and cations interacted with the perovskite interfacial layer.…”

“…For instance, NH 4 F treatment modified surface hydroxyl groups by inducing Sn–F chemical bonding via capturing the surface hydroxyl anions by NH 4+ , 14 and for the case of zwitterions, 17 anions were anchored on the SnO 2 surface and cations interacted with the perovskite interfacial layer. Besides reducing trap state by passivation, the strategy of lowering the SnO 2 /perovskite interfacial energy barrier was attempted by using benzylamine hydrochloride 22 and phosphate. 23 Those studies indicate that bifunctionality of the passivation agents plays an important role at heterogeneous interface.…”