No abstract

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 built‐in electric field (BEF) intensity of silicon heterojunction solar cells can be easily enhanced by selective doping to obtain high power conversion efficiencies (PCEs), while it is challenging for perovskite solar cells (pero‐SCs) because of the difficulty in doping perovskites in a controllable way. Herein, an effective method is reported to enhance the BEF of FA0.92MA0.08PbI3 perovskite by doping an organic ferroelectric material, poly(vinylidene fluoride):dabcoHReO4 (PVDF:DH) with high polarizability, that can be driven even by the BEF of the device itself. The polarization of PVDF:DH produces an additional electric field, which is maintained permanently, in a direction consistent with that of the BEF of the pero‐SC. The BEF superposition can more sufficiently drive the charge‐carrier transport and extraction, thus suppressing the nonradiative recombination occurring in the pero‐SCs. Moreover, the PVDF:DH dopant benefits the formation of a mesoporous PbI2 film, via a typical two‐step processing method, thereby promoting perovskite growth with high crystallinity and a few defects. The resulting pero‐SC shows a promising PCE of 24.23% for a 0.062 cm2 device (certified PCE of 23.45%), and a remarkable PCE of 22.69% for a 1 cm2 device, along with significantly improved moisture resistances and operational stabilities.

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.

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%.