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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 1cm 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.

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 À ) ions, to stabilize the whole device fabrication process. The C=O and Se + can coordinate with lead and iodine (I À ) 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 À efficiently suppress the dissociation and migration of I À 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 15.39cm 2 module, respectively. The devices retained over 90 % of their initial efficiency under operation for 2200 h.

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Figure 5. Stability test of the unencapsulated flexible pero-SCs based on Pero-C, Pero-N, and Pero-I a) versus bending cycles at a radius of 5 mm, b) and at MPP under a 100 mW cm −2 white light-emitting diode stored in an N 2 atmosphere. c) Summary of the comprehensive device performance of the flexible pero-SCs with PCEs >22.5%.