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To date, perovskite solar cells (pero‐SCs) with doped 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) hole transporting layers (HTLs) have shown the highest recorded power conversion efficiencies (PCEs). However, their commercialization is still impeded by poor device stability owing to the hygroscopic lithium bis(trifluoromethanesulfonyl)imide and volatile 4‐tert‐butylpyridine dopants as well as time‐consuming oxidation in air. In this study, we explored a series of single‐component iodonium initiators with strong oxidability and different electron delocalization properties to precisely manipulate the oxidation states of Spiro‐OMeTAD without air assistance, and the oxidation mechanism was clearly understood. Iodine (III) in the diphenyliodonium cation (IP+) can accept a single electron from Spiro‐OMeTAD and forms Spiro‐OMeTAD⋅+ owing to its strong oxidability. Moreover, because of the coordination of the strongly delocalized TFSI− with Spiro‐OMeTAD⋅+ in a stable radical complex, the resulting hole mobility was 30 times higher than that of pristine Spiro‐OMeTAD. In addition, the IP‐TFSI initiator facilitated the growth of a homogeneous and pinhole‐free Spiro‐OMeTAD film. The pero‐SCs based on this oxidizing HTL showed excellent efficiencies of 25.16 % (certified: 24.85 % for 0.062‐cm2) and 20.71 % for a 15.03‐cm2 module as well as remarkable overall stability. [ABSTRACT FROM AUTHOR]

The use of dopant-free hole transport layers (HTLs) is critical in stabilizing n-i-p perovskite solar cells (pero-SCs). However, these HTL materials are often processed with toxic solvents, which is not ideal for industrial production. Upon substituting them with green solvents, a trade-off emerges between maintaining the high crystallinity of the HTL materials and ensuring high solubility in the new solvents. In this paper, we designed a novel, linear, organic small molecule, BDT-C8-3O, by introducing an asymmetric polar oligo(ethylene glycol) side chain. This method not only overcomes the solubility limitations in green solvents but also enables stacking the conjugated main chains in two patterns, which further enhances crystallinity and hole mobility. As a result, the n-i-p pero-SCs based on chlorobenzene- or green (natural compound) solvent 3-methylcyclohexanone-processed BDT-C8-3O HTL that without any dopant delivered world-recorded power conversion efficiencies of 24.11 % (certified of 23.82 %) and 23.53 %, respectively. The devices also demonstrated remarkable operational and high-temperature stabilities, maintaining over 84 % and 79.5 % of their initial efficiency for 2000 h, respectively. Encouragingly, dopant-free BDT-C8-3O HTL exhibits significant advantages in large-area fabrication, achieving state-of-the-art PCEs exceeding 20 % for 5×5 cm 2 modules (active area: 15.64 cm 2 ), even when processed using green solvents., (© 2023 Wiley-VCH GmbH.)

The stability-related issues arising from the perovskite precursor inks, films, device structures and interdependence remain severely under-explored to date. Herein, we designed an ionic-liquid polymer (poly[Se-MI][BF 4 ]), containing functional moieties like carbonyl (C=O), selenium (Se + ), and tetrafluoroborate (BF 4 - ) ions, to stabilize the whole device fabrication process. The C=O and Se + can coordinate with lead and iodine (I - ) ions to stabilize lead polyhalide colloids and the compositions of the perovskite precursor inks for over two months. The Se + anchored on grain boundaries and the defects passivated by BF 4 - efficiently suppress the dissociation and migration of I - in perovskite films. Benefiting from the synergistic effects of poly[Se-MI][BF 4 ], high efficiencies of 25.10 % and 20.85 % were exhibited by a 0.062-cm 2 device and 15.39-cm 2 module, respectively. The devices retained over 90 % of their initial efficiency under operation for 2200 h., (© 2023 Wiley-VCH GmbH.)

Dopant-free organic hole transport materials (HTMs) remain highly desirable for stable and efficient n-i-p perovskite solar cells (pero-SCs) but rarely succeed. Here, we propose a molecular assembly strategy to overcome the limited optoelectronic properties of organic HTMs by precisely designing a linear organic small molecule BDT-DPA-F from the atomic to the molecular levels. BDT-DPA-F can assemble into a fibril network, showing an obviously improved hole mobility and decreased energy disorder. The resultant pero-SCs showed a promising efficiency of 23.12 % (certified 22.48 %), which is the highest certified value of pero-SCs with dopant-free HTMs, to date. These devices also showed a weak-dependence of efficiency on size, enabling a state-of-the-art efficiency of 22.50 % for 1-cm 2 device and 20.17 % for 15.64-cm 2 module. For the first time, the pero-SCs based on dopant-free HTMs realized ultralong stabilities with T 80 lifetimes over 1200 h under operation or thermal aging at 85 °C., (© 2022 Wiley-VCH GmbH.)