Hole transport layer (HTL) is very important for the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). As current state‐of‐the‐art HTL, Li‐TFSI doped spiro‐OMeTAD often suffers low conductivity and the hydrolysis of the additive Li‐TFSI, which significantly hinders the further improvement of PCE of PSCs. Besides, conventional spiro‐OMeTAD has no functional of directly passivating the perovskite crystal defects. Herein, multifunctional TiO2nanoparticles (NPs)‐modified CNT (CNT:TiO2) doped spiro‐OMeTAD (spiro‐OMeTAD+CNT:TiO2) HTL is reported for the first time. The incorporated CNT:TiO2not only significantly increases the conductivity of spiro‐OMeTAD+CNT:TiO2, but also effectively passivates the crystal defects of perovskite layer. The optimized PSCs with spiro‐OMeTAD+CNT:TiO2HTL achieved a peak PCE of 21.53%, much higher than that (17.90%) of the conventional spiro‐OMeTAD based PSCs and also show significantly improved stability.
- Award ID(s):
- 1824674
- NSF-PAR ID:
- 10294412
- Date Published:
- Journal Name:
- Energy & Environmental Science
- Volume:
- 13
- Issue:
- 11
- ISSN:
- 1754-5692
- Page Range / eLocation ID:
- 4334 to 4343
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We report design principles of the thermal and redox properties of synthetically accessible spiro‐based hole transport materials (HTMs) and show the relevance of these findings to high‐performance perovskite solar cells (PSCs). The chemical modification of an asymmetric spiro[fluorene‐9,9′‐xanthene] core is amenable to selective placement of redox active triphenylamine (TPA) units. We therefore leveraged computational techniques to investigate five HTMs bearing TPA groups judiciously positioned about this asymmetric spiro core. It was determined that TPA groups positioned about the conjugated fluorene moiety increase the free energy change for hole‐extraction from the perovskite layer, while TPAs about the xanthene unit govern the
T gvalues. The synergistic effects of these characteristics resulted in an HTM characterized by both a low reduction potential (≈0.7 V vs. NHE) and a highT gvalue (>125 °C) to yield a device power conversion efficiency (PCE) of 20.8 % in a PSC. -
Abstract We report design principles of the thermal and redox properties of synthetically accessible spiro‐based hole transport materials (HTMs) and show the relevance of these findings to high‐performance perovskite solar cells (PSCs). The chemical modification of an asymmetric spiro[fluorene‐9,9′‐xanthene] core is amenable to selective placement of redox active triphenylamine (TPA) units. We therefore leveraged computational techniques to investigate five HTMs bearing TPA groups judiciously positioned about this asymmetric spiro core. It was determined that TPA groups positioned about the conjugated fluorene moiety increase the free energy change for hole‐extraction from the perovskite layer, while TPAs about the xanthene unit govern the
T gvalues. The synergistic effects of these characteristics resulted in an HTM characterized by both a low reduction potential (≈0.7 V vs. NHE) and a highT gvalue (>125 °C) to yield a device power conversion efficiency (PCE) of 20.8 % in a PSC. -
Improving efficiency and stability has become an urgent issue in the application of perovskite solar cells (PSCs). Herein, a kind of long‐chain polymer or polymethylmethacrylate (PMMA) is added into the spiro‐OMeTAD matrix to improve the film formation process and hence the device performance. It is observed that, after modification, the spiro‐OMeTAD‐based hole‐transporting layer becomes uniform, continuous, and condensed. Meanwhile, the power conversion efficiency of the devices is upgraded. Compared with the control device, open‐circuit voltage of the modified one (with moderate doping) increases from 1.06 (±0.03) to 1.10 (±0.02) V, fill factor increases from 72.20 (±3.44)% to 75.59 (±3.35)%, and the power conversion efficiency increases from 18.82 (±1.06)% to 20.51 (±0.82)% (highest at 21.78%) under standard test condition (AM 1.5G, 100 mW cm−2). Transient photocurrent/photovoltage decay curves, time‐resolved photoluminance, and impedance spectroscopy studies show that the modification could accelerate charge transfer and retard interfacial recombination. In addition, the modification improves device stability. Due to the strengthened barrier against penetration of “H2O/O2/Ag,” the efficiency of the unsealed device could retain 91.49% (by average) of the initial one after 100 days storage in the dark [relative humidity = 30(±5)%]. This work shows that long‐chain polymer doping could simultaneously improve efficiency and stability of spiro‐OMeTAD‐based PSCs.
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Abstract Flexible perovskite solar cells (
f ‐PSCs) have attracted great attention due to their promising commercial prospects. However, the performance off ‐PSCs is generally worse than that of their rigid counterparts. Herein, it is found that the unsatisfactory performance of planar heterojunction (PHJ)f ‐PSCs can be attributed to the undesirable morphology of electron transport layer (ETL), which results from the rough surface of the flexible substrate. Precise control over the thickness and morphology of ETL tin dioxide (SnO2) not only reduces the reflectance of the indium tin oxide (ITO) on polyethylene 2,6‐naphthalate (PEN) substrate and enhances photon collection, but also decreases the trap‐state densities of perovskite films and the charge transfer resistance, leading to a great enhancement of device performance. Consequently, thef ‐PSCs, with a structure of PEN/ITO/SnO2/perovskite/Spiro‐OMeTAD/Ag, exhibit a power conversion efficiency (PCE) up to 19.51% and a steady output of 19.01%. Furthermore, thef ‐PSCs show a robust bending resistance and maintain about 95% of initial PCE after 6000 bending cycles at a bending radius of 8 mm, and they present an outstanding long‐term stability and retain about 90% of the initial performance after >1000 h storage in air (10% relative humidity) without encapsulation.