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.

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Since the discovery of piezoelectricity in poly(vinylidene fluoride) (PVDF) 50 years ago, ferroelectric polymers have established their own areas for research and applications due to their unique properties in comparison to single crystals and inorganics. PVDF is a semicrystalline polymer that can crystallize into five different polymorphs. Among them, the polar β-phase is the most interesting one for electroactive properties because it has the highest dipolar moment and the highest piezoelectric response. In the early days, the β-PVDF was typically produced by melt processing, limiting its form to free-standing films. The rapid development of flexible electronics, however, highly requires β-PVDF fabricated from solutions under mild conditions. The objective of this perspective is to summarize the effective methods to produce β-PVDF from solution, to present the approaches for enhancing the electroactive properties through morphological controls, and to discuss the applications of PVDF-based ferroelectric polymers in flexible electronics. In addition, current challenges that may impede the further development of this field are pointed out.

This article models the contact between the drillstring with large slenderness ratio and the extending rigid wellbore based on the multibody dynamics method. The drillstring is modeled as absolute nodal coordinate formulation beams with contact detection points. An algorithm is developed to locate the contact points and calculate the contact forces when the drillstring is sliding and rotating in the wellbore. This provides support force and friction for the moving drillstring and effectively confines it inside the wellbore. A rock penetration model is established based on the rock-breaking velocity equation. The governing equation for the full-hole drilling system including the drillstring and the contact model is established and solved. A rock penetration correction method is proposed to stabilize the computation and to model and simulate the slide drilling process. A field drilling process is modeled and simulated. The simulation result fits the experimental result well.

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