Organic Hole Transport Material Ionization Potential Dictates Diffusion Kinetics of Iodine Species in Halide Perovskite Devices

Kerner, Ross A.; Heo, Sungyeon; Roh, Kwangdong; MacMillan, Kyle; Larson, Bryon W.; Rand, Barry P.

doi:10.1021/acsenergylett.0c02495

Cited by 41 publications

(63 citation statements)

References 68 publications

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“…As we discussed previously, postoxidation of spiro-OMeTAD by iodine gas is detrimental for the stability, especially at high temperature. This phenomena was observed in recent work by Kerner et al 84 They observed not only the oxidation of spiro-OMeTAD but also the oxidation of several organic HTL materials. They found that the HOMO levels of organic HTLs are affected by the oxidation process by iodine gases.…”

Section: ■ Challenges and Perspectivessupporting

confidence: 70%

Mini-Review on Efficiency and Stability of Perovskite Solar Cells with Spiro-OMeTAD Hole Transport Layer: Recent Progress and Perspectives

2021

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Organic–inorganic metal halide perovskite solar cells (PSCs) are one of the emerging technologies in photovoltaic research. The certified maximum power conversion efficiency (PCE) of PSCs has reached as high as 25%. In particular, the development of hole transport layer (HTL) materials plays a key role in increasing PCEs. Among a vast number of HTL materials developed to date, the most common HTL material is 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), because it can provide very high performance in PSCs. Besides the high PCE, the issue of long-term stability is of paramount importance. The room-temperature operational stability of PSCs with the spiro-OMeTAD HTL has been improved significantly past few years, but it is still low, compared with Si-based technology. In addition, the instability at high temperature is the Achilles heel of PSCs with the spiro-OMeTAD HTL. Although the low operational stability of PSCs, especially at high temperature, is generally associated with instability of spiro-OMeTAD, the high-temperature stability has been improved significantly by understanding the degradation mechanisms. In this mini-review, we discuss the degradation mechanisms and suggest our perspectives to overcome the degradation. Thus, this mini-review will guide the development of stable PSCs with the spiro-OMeTAD HTL and the design of new HTL materials to replace spiro-OMeTAD toward commercialization of PSCs in the future.

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Section: ■ Challenges and Perspectivessupporting

confidence: 70%

Mini-Review on Efficiency and Stability of Perovskite Solar Cells with Spiro-OMeTAD Hole Transport Layer: Recent Progress and Perspectives

2021

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“…We have also demonstrated that spiro‐MeOTAD can be doped by iodine sourced from I 2 vapor as well as released from the perovskite layer, resulting in increased conductivity, and displaying fast iodine/triiodide permeation rates. [ 18 ] In the device structure probed here, we exploit the ease of measuring conductivity changes in the initially undoped spiro‐MeOTAD, taking it as an indicator for iodide released from the perovskite layer. Once liberated, iodine/triiodide/iodide within the spiro‐MeOTAD is much more mobile, capable of migrating vertically and laterally to influence many observables including halide segregation.…”

Section: Resultsmentioning

confidence: 99%

Iodine Electrochemistry Dictates Voltage‐Induced Halide Segregation Thresholds in Mixed‐Halide Perovskite Devices

Kerner

Berry

et al. 2022

Adv Funct Materials

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Owing to straightforward stoichiometry-bandgap tunability, mixed-halide perovskites are ideal for many optoelectronic devices. However, unwanted halide segregation under operational conditions, including light illumination and voltage bias, restricts practical use. Additionally, the origin of voltageinduced halide segregation is still unclear. Herein, a systematic voltage threshold study in mixed bromide/iodide perovskite devices is performed and leads to observation of three distinct voltage thresholds corresponding to the doping of the hole transport material (0.7 ± 0.1 V), halide segregation (0.95 ± 0.05 V), and degradation (1.15 ± 0.05 V) for an optically stable mixed-halide perovskite composition with a low bromide content (10%). These empirical threshold voltages are minimally affected by composition until very Br-rich compositions, which reveals the dominant role of iodide/triiodide/iodine electrochemistry in voltage-induced Br/I phase separation and transport layer doping reactions in halide perovskite devices.

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“…It is due to the hydrophobic nature of the polymeric HTLs without dopants that they can protect the underlying perovskites from water. [ 60 ]…”

Section: Resultsmentioning

confidence: 99%

Donor–Acceptor Type Polymer Bearing Carbazole Side Chain for Efficient Dopant‐Free Perovskite Solar Cells

You

Wang

et al. 2021

Advanced Energy Materials

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In conventional n–i–p perovskite solar cells (PVSCs), electron donor (D)–acceptor (A) polymers have been found to be potential substitutes for doped spiro‐based small molecule hole‐transporting materials (HTMs) due to their excellent performance in hole mobility, film formability, and stability. Herein, a benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐benzodithiophene‐4,8‐dione (BDD) copolymer PBDB‐Cz is developed by employing carbazole as the conjugated side chain of BDT. PBDB‐O and PBDB‐T with alkoxy and thiophene as the side chain of BDT, respectively, are also synthesized and studied for comparison. The synergistic effect of the carbazole side chain and the BDT‐BDD backbone to promote hole transport properties is found in PBDB‐Cz. The carbazole side chain enhances both coplanarity and interaction of polymer chains, while simultaneously deepening energy levels and improving the hole mobility of the polymeric HTM. Consequently, PBDB‐Cz outperforms two counterparts, exhibiting a promising power conversion efficiency (PCE) of 22.06%. Notably, the PBDB‐Cz also improves the device stability, and the devices can retain more than 90% of their initial PCEs after being stored at ambient conditions for 100 days. To the best of the authors’ knowledge, this is the first report to incorporate carbazole into D–A polymeric HTM by side chain engineering.

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Organic Hole Transport Material Ionization Potential Dictates Diffusion Kinetics of Iodine Species in Halide Perovskite Devices

Cited by 41 publications

References 68 publications

Mini-Review on Efficiency and Stability of Perovskite Solar Cells with Spiro-OMeTAD Hole Transport Layer: Recent Progress and Perspectives

Mini-Review on Efficiency and Stability of Perovskite Solar Cells with Spiro-OMeTAD Hole Transport Layer: Recent Progress and Perspectives

Iodine Electrochemistry Dictates Voltage‐Induced Halide Segregation Thresholds in Mixed‐Halide Perovskite Devices

Donor–Acceptor Type Polymer Bearing Carbazole Side Chain for Efficient Dopant‐Free Perovskite Solar Cells

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