The variation of the vertical component distribution can significantly influence the photovoltaic performance of organic solar cells (OSCs), mainly due to its impact on exciton dissociation and charge‐carrier transport and recombination. Herein, binary devices are fabricated via sequential deposition (SD) of D18 and L8‐BO materials in a two‐step process. Upon independently regulating the spin‐coating speeds of each layer deposition, the optimal SD device shows a record power conversion efficiency (PCE) of 19.05% for binary single‐junction OSCs, much higher than that of the corresponding blend casting (BC) device (18.14%). Impressively, this strategy presents excellent universality in boosting the photovoltaic performance of SD devices, exemplified by several nonfullerene acceptor systems. The mechanism studies reveal that the SD device with preferred vertical components distribution possesses high crystallinity, efficient exciton splitting, low energy loss, and balanced charge transport, resulting in all‐around enhancement of photovoltaic performances. This work provides a valuable approach for high‐efficiency OSCs, shedding light on understanding the relationship between photovoltaic performance and vertical component distribution.

Binary Organic Solar Cells Breaking 19% via Manipulating the Vertical Component Distribution

The large energy loss (Eloss) is one of the main obstacles to further improve the photovoltaic performance of organic solar cells (OSCs), which is closely related to the charge transfer (CT) state. Herein, ternary donor alloy strategy is used to precisely tune the energy of CT state (ECT) and thus the Eloss for boosting the efficiency of OSCs. The elevated ECT in the ternary OSCs reduce the energy loss for charge generation (ΔECT), and promote the hybridization between localized excitation state and CT state to reduce the nonradiative energy loss (ΔEnonrad). Together with the optimal morphology, the ternary OSCs afford an impressive power conversion efficiency of 19.22% with a significantly improved open‐circuit voltage (Voc) of 0.910 V without sacrificing short‐cicuit density (Jsc) and fill factor (FF) in comparison to the binary ones. This contribution reveals that precisely tuning the ECT via donor alloy strategy is an efficient way to minimize Eloss and improve the photovoltaic performance of OSCs.

Over 19.2% Efficiency of Organic Solar Cells Enabled by Precisely Tuning the Charge Transfer State Via Donor Alloy Strategy

The structural order and aggregation of non‐fullerene acceptors (NFA) are critical toward light absorption, phase separation, and charge transport properties of their photovoltaic blends with electron donors, and determine the power conversion efficiency (PCE) of the corresponding organic solar cells (OSCs). In this work, the fibrillization of small molecular NFA L8‐BO with the assistance of fused‐ring solvent additive 1‐fluoronaphthalene (FN) to substantially improve device PCE is demonstrated. Molecular dynamics simulations show that FN attaches to the backbone of L8‐BO as the molecular bridge to enhance the intermolecular packing , inducing 1D self‐assembly of L8‐BO into fine fibrils with a compact polycrystal structure. The L8‐BO fibrils are incorporated into a pseudo‐bulk heterojunction (P‐BHJ) active layer with D18 as a donor, and show enhanced light absorption, charge transport, and collection properties, leading to enhanced PCE from 16.0% to an unprecedented 19.0% in the D18/L8‐BO binary P‐BHJ OSC, featuring a high fill factor of 80%. This work demonstrates a strategy for fibrillating NFAs toward the enhanced performance of OSCs.

Fibrillization of Non‐Fullerene Acceptors Enables 19% Efficiency Pseudo‐Bulk Heterojunction Organic Solar Cells

Symmetric-breaking strategy has broadly applied in organic photovoltaic material design while a comprehensive understanding of the effects of two dimension (2D) asymmetric side chains in all-small-molecule organic solar cells (ASM-OSCs)...

Over 17% efficiency all-small-molecule organic solar cells based on an organic molecular donor employing 2D side chain symmetric-breaking strategy

Research on organic solar cells (OSCs) has progressed through material innovation and device engineering. However, well‐known and ubiquitous intermolecular interactions, and particularly their synergistic effects, have received little attention. Herein, the complicated relationship between photovoltaic conversion and multidimensional intermolecular interactions in the active layers is investigated. These interactions are dually regulated by side‐chain isomerization and end‐cap engineering of the acceptors. The phenylalkyl featured acceptors (LA‐series) exhibit stronger crystallinity with preferential face‐on interactions relative to the alkylphenyl attached isomers (ITIC‐series). In addition, the PM6 and LA‐series acceptors exhibit moderate donor/acceptor interactions compared to those of the strongly interacting PM6/ITIC‐series pairs, which helps to enhance phase separation and charge transport. Consequently, the output efficiencies of all LA series acceptors are over 14%. Moreover, LA‐series acceptors show appropriate compatibility, host/guest interactions, and crystallinity relationships with BTP‐eC9, thereby leading to uniform and well‐organized “alloy‐like” mixed phases. In particular, the highly crystalline LA23 further optimizes multiple interactions and ternary microstructures, which results in a high efficiency of 19.12%. Thus, these results highlight the importance of multidimensional intermolecular interactions in the photovoltaic performance of OSCs.

Over 19% Efficiency Organic Solar Cells by Regulating Multidimensional Intermolecular Interactions

Volatile solid additives (SADs) are considered as a simple yet effective approach to tune the film morphology for high-performance organic solar cells (OSCs). However, the structural effects of the SADs on the photovoltaic performance are still elusive. Herein, two volatilizable SADs were designed and synthesized. One is SAD1 with twisted conformation, while the other one is planar SAD2 with the S···O noncovalent intramolecular interactions (NIIs). The theoretical and experimental results revealed that the planar SAD2 with smaller space occupation can more easily insert between the Y6 molecules, which is beneficial to form a tighter intermolecular packing mode of Y6 after thermal treatment. As a result, the SAD2-treated OSCs exhibited less recombination loss, more balanced charge mobility, higher hole transfer rate, and more favorable morphology, resulting in a record power conversion efficiency (PCE) of 18.85% (certified PCE: 18.7%) for single-junction binary OSCs. The universality of this study shed light on understanding the conformation effects of SADs on photovoltaic performances of OSCs.

https://pubs.acs.org/doi/pdf/10.1021/jacs.2c05303

Achieving Record-Efficiency Organic Solar Cells upon Tuning the Conformation of Solid Additives

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have surpassed 19% thanks to the innovation of polymer donors and molecular acceptors. However, the batch‐to‐batch variations in polymer materials are detrimental to the reproducibility of the device performance. In comparison, small‐molecule donors (SMDs) possess some unique advantages, such as well‐defined molecular weights, easy purification, and excellent batch‐to‐batch repeatability. Herein, a pair of regioisomeric SMDs (BT‐O1 and BT‐O2) has been synthesized with alkoxy groups as S···O noncovalently conformational locks (NoCLs) at the inner and outer position, respectively. Theoretical and experimental results reveal that the regioisomeric effect has a significant influence on the light‐harvest ability, energy levels, molecular geometries, internal reorganization energy, and packing behaviors for the two SMDs. As a result, BT‐O2‐based binary device shows an impressive PCE of 13.99%, much higher than that of BT‐O1 based one (4.07%), due to the better‐aligned energy level, more balanced charge transport, less charge recombination, lower energy loss, and more favorable phase separation. Furthermore, the fullerene derivative PC71BM is introduced into BT‐O2:H3 as the third component to achieve a notable PCE of 15.34% (certified 14.6%). Overall, this work reveals that NoCLs is a promising strategy to achieve high‐performance SMDs for all‐small‐molecule OSCs.

Xiaobin Gu

Papers

Binary Organic Solar Cells Breaking 19% via Manipulating the Vertical Component Distribution

Achieving Record-Efficiency Organic Solar Cells upon Tuning the Conformation of Solid Additives

Over 19.2% Efficiency of Organic Solar Cells Enabled by Precisely Tuning the Charge Transfer State Via Donor Alloy Strategy

High‐Performance All‐Small‐Molecule Organic Solar Cells Enabled by Regio‐Isomerization of Noncovalently Conformational Locks

Low-cost polymer acceptors with noncovalently fused-ring backbones for efficient all-polymer solar cells