Abstract
Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo[1,2-b:4,5-b’]dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor–acceptor (D–A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π–π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the “Lewis soft” selenium atom can passivate surface trap sites of perovskite films by Pb–Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.
Highlights
Perovskite solar cells (PSCs) have gone through an unprecedented increase in power conversion efficiency (PCE) from a mere 3.8% to 25.2% in the past decade due to the excellent light-harvesting capacity and unrivalled chargecarrier diffusion length of organic−inorganic hybrid lead halide perovskites.[1−9] In spite of the rapidly surging PCE, PSCs have caused extensive scientific studies because of their exceptional photoelectric character, facile processability, and promising commercial potential.[10−12] Recently, perovskite/Si tandem devices surpassed crystalline Si photovoltaics, displaying an exciting PCE of 29.1%, greatly boosting PSCs toward the ultimate aim of economic feasibility.[9]
Compared to some other holetransport materials (HTMs) used in PSCs, such as small molecules or inorganic materials, polymeric HTMs possess several advantages involving excellent carrier mobility, thermal and optical stability, solution processability, film-forming ability, and potential industrial production through roll-to-roll printing technologies.[47−49] far, several dopant-free polymeric HTMs have been applied in PSCs and contributed to relatively high PCEs and significantly enhanced device stability.[50−57] most known materials feature a strong donor− acceptor (D−A) structure inherited from the polymeric donors in bulk heterojunction organic solar cells (OSCs)
We synthesized a series of novel and costeffective polymeric semiconductors PC1, PC2, and PC3 characterized by a rigid PC plane and explored their application as dopant-free HTMs in PSCs
Summary
Perovskite solar cells (PSCs) have gone through an unprecedented increase in power conversion efficiency (PCE) from a mere 3.8% to 25.2% in the past decade due to the excellent light-harvesting capacity and unrivalled chargecarrier diffusion length of organic−inorganic hybrid lead halide perovskites.[1−9] In spite of the rapidly surging PCE, PSCs have caused extensive scientific studies because of their exceptional photoelectric character, facile processability, and promising commercial potential.[10−12] Recently, perovskite/Si tandem devices surpassed crystalline Si photovoltaics, displaying an exciting PCE of 29.1%, greatly boosting PSCs toward the ultimate aim of economic feasibility.[9]. Compared to some other HTMs used in PSCs, such as small molecules or inorganic materials, polymeric HTMs possess several advantages involving excellent carrier mobility, thermal and optical stability, solution processability, film-forming ability, and potential industrial production through roll-to-roll printing technologies.[47−49] far, several dopant-free polymeric HTMs have been applied in PSCs and contributed to relatively high PCEs and significantly enhanced device stability.[50−57] most known materials feature a strong donor− acceptor (D−A) structure inherited from the polymeric donors in bulk heterojunction organic solar cells (OSCs). The guiding principles for rational design of dopant-free polymeric HTMs are illustrated in this work
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