A new, easy, and efficient approach is reported to enhance the driving force for charge transfer, break tradeoff between open-circuit voltage and short-circuit current, and simultaneously achieve very small energy loss (0.55 eV), very high open-circuit voltage (>1 V), and very high efficiency (>10%) in fullerene-free organic solar cells via an energy driver.
The unidirectional extension of a smaller fused-ring system into a larger one in a single direction will increase the conjugation length, allowing a fine-tuning of electronic properties. Here, we designed and synthesized a unidirectionally extended fused-8-ring-based nonfullerene acceptor, AOIC, and a bidirectionally extended fused-11-ring electron acceptor, IUIC2, and compared these with the parent fused-5-ring electron acceptor, F5IC. They share the same electron-accepting groups and alkylphenyl side chains but have different fused-ring electrondonating units. Core extension from 5 to 11 rings up-shifts the energy levels, red shifts the absorption spectra, and reduces bandgaps. The unidirectionally extended AOIC has the highest mobility (2.1 × 10 −3 cm 2 V −1 s −1) relative to the parent F5IC (1.0 × 10 −3 cm 2 V −1 s −1) and the bidirectionally extended IUIC2 (4.7 × 10 −4 cm 2 V −1 s −1). Upon blending with the donor PTB7-Th, AOIC-based organic photovoltaic cells show an efficiency of 13.7%, much better than that of F5IC-based cells (5.61%) and IUIC2-based cells (4.48%).
We report the fused ring electron acceptor (FREA)− perovskite hybrid as a promising platform to fabricate organic−inorganic hybrid solar cells with simple preparation, high efficiency, and good stability. The FREA−perovskite hybrid films exhibit larger grain sizes and stronger crystallinity than the pristine perovskite films. Moreover, the FREA molecules can form coordination bonding with undercoordinated Pb atoms and passivate the trap states in the perovskite films. Time-resolved photoluminescence and transient absorption measurements reveal that FREA facilitates efficient electron extraction and collection. Transient photocurrent and photovoltage measurements suggest faster charge transfer and reduced charge recombination in solar cells based on FREA− perovskite hybrid films. Consequently, solar cells based on FREA− perovskite hybrid films yield a champion efficiency of 21.7% with enhanced stability, which is higher than that of the control devices based on pristine perovskite films (19.6%).
rials and perovskite, or between chargetransport materials and the electrodes.Fullerene and derivatives are the n-type organic semiconductors first used in PSCs, and possess some merits, such as suitable energy level alignment, high electron mobility, and trap-passivation function. [16][17][18][19][20] In general, fullerenes mainly serve as ETM, and are gradually used as interface-modifying materials and additives in PSCs. [21][22][23][24][25][26][27][28][29][30][31] Nevertheless, fullerenes have some drawbacks, such as limited energy level variation, thermal instability and photochemical instability, difficult purification, and poor flexibility. To overcome deficiencies of fullerenes, nonfullerene organic semiconductors were incorporated into PSCs. In particular, rylene diimides and fused-ring electron acceptors (FREAs) are two best-performing classes of nonfullerene acceptors used in organic solar cells (OSCs), [32,33] and therefore are widely used in PSCs.The chemical structure of nonfullerene organic semiconductors can be facilely tailored, and therefore, the electronic, optical, and morphological characteristics of the materials can be precisely modulated, providing potential benefits to PSCs. First, the energy levels of nonfullerenes can be tuned to match well with that of perovskite materials, facilitating efficient charge extraction and transport; second, the intense absorption of nonfullerenes in the near-infrared (NIR) region can complement that of perovskite, leading to panchromatic absorption; third, various functional groups in nonfullerene molecules can supply lone-pair electrons for defect passivation. In addition, nonfullerene organic semiconductors have excellent morphological stability.This research news summarizes the recent progress of nonfullerene n-type organic semiconductors in terms of electrontransporting materials, interface-modifying materials, additives, and light-harvesting materials used in both normal and inverted PSCs. The effects of nonfullerene materials on device efficiency and stability are discussed. Finally, the remaining key challenges and promising future research directions of nonfullerene-based PSCs are also proposed. Electron-Transporting MaterialsFunctions of ETM are to extract electrons from perovskite layer and transport electrons to the cathode and block holes to reduce the carrier recombination. Basic requirements for ETM are: a) suitable lowest unoccupied molecular orbital (LUMO)/ highest occupied molecular orbital (HOMO) energy levels Compared to inorganic semiconductors and/or fullerene derivatives, nonfullerene n-type organic semiconductors present some advantages, such as low-temperature processing, flexibility, and molecule structure diversity, and have been widely used in perovskite solar cells (PSCs). In this research news article, the recent advances in nonfullerene n-type organic semiconductors which function as electron-transporting, interfacemodifying, additive, and light-harvesting materials in PSCs are summarized. The remaining challenges and promising...
A low temperature processed fused-ring electron acceptor IDIC is used as the electron transport layer in planar n–i–p perovskite solar cells, which exhibit higher efficiency and better stability than control devices based on TiO2.
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