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In addition to high power conversion efficiency (PCE) and good stability, the low-cost of photovoltaic materials is also very important for the practical application of organic solar cells (OSCs). Herein, we synthesized a carboxylate substituted pyrazine-based electron-deficient building block (DTCPz) with a simple structure and low synthetic cost, and then developed a novel wide bandgap polymer donor PFBCPZ. Due to the synergistic electron-withdrawing effects of the fluorination in donor unit (BDT-TF) and esterification and C=N double-bond in DTCPz unit, PFBCPZ shows a deeper HOMO level of −5.60 eV, a strong intermolecular π-π interaction, good crystallinity and stacking, and high hole-mobility of 2.11 × 10−3 cm2 V−1 s−1. Matched with a low bandgap acceptor IT-4F, excellent charge transfer, weak recombination, and small non-radiative energy loss in OSCs was achieved, resulting in an impressive fill factor of 0.785 and a high open-circuit voltage of 0.92 V. As a result, a PCE of up to 15.3% is obtained in OSCs, which is the highest value in the IT-4F-based binary OSCs so far and indicates that low-cost DTCPz with a simple structure is a promising building block to construct high-performance polymer donors for application in efficient OSCs. [Display omitted] • A novel wide bandgap polymer donor PFBCPZ was synthesized. • The novel building block (DTCPz) showed easily synthesized routs with cheap raw material. • The OSC based on PFBCPZ:IT-4F exhibited excellent performance with 15.3% efficiency. • The efficiency is the highest value in the IT-4F-based binary OSCs so far. [ABSTRACT FROM AUTHOR]

Simultaneously broadening the spectral response and reducing the energy loss are challenging tasks in the material design of organic solar cells (OSCs). Herein, a novel asymmetrically noncovalently fused-ring electron acceptor (NFEA) with unilateral alkylthio-substituted thiophene π-bridge, namely IDST-4F, is synthesized. IDST-4F exhibits a broader absorption, higher-lying energy levels, larger dipole moments and suppressed crystallinity than its symmetric counterpart (ID-4F) without the π-bridge. Compared to the devices of PM6:ID-4F, the optimized PM6:IDST-4F-based devices display simultaneously enhanced current density and photovoltage, resulting in an excellent power conversion efficiency (PCE) of 14.3%, which is the highest value among the OSCs based on NFEAs reported in the literature to date. More importantly, the PM6:IDST-4F-based OSCs possess excellent thermal stability with 82% of the initial PCE after thermal treatment at 150 °C for 1200 min. In summary, this study indicates that asymmetrically NFEAs are promising to achieve high efficiency with excellent thermal stability. Image 1 • A novel acceptor IDST-4F, consisting of an asymmetric fused-ring core locked by a noncovalent interaction is developed. • The PM6:IDST-4F-based OSCs display a significantly improved efficiency of 14.3%. • The PM6:IDST-4F-based PSCs exhibit lower energy loss of 0.59 eV and excellent thermal stability. [ABSTRACT FROM AUTHOR]

• Acceptor fluorination leads to increased voltage losses in organic solar cells. • The increased voltage loss is associated with increased reorganization energy. • A side chain modification strategy is proposed to address the voltage loss issue. Acceptor fluorination is a commonly employed molecular modification strategy aimed at enhancing the quantum efficiency and charge carrier transport properties of organic solar cells. However, this approach often leads to a significant reduction in the open-circuit voltage (V oc) of the solar cells, thereby limiting their overall performance. In this study, we investigate the limitation of V oc in organic solar cells based on fluorinated acceptors. Our investigation reveals that the reduced V oc can be attributed to increased voltage losses (V loss), primarily arising from more significant non-radiative voltage losses originating from a decline in the external quantum efficiency of electroluminescence (EQE EL). Furthermore, we establish that the reduced EQE EL is a result of deteriorated molecular packing, which leads to an elevated reorganization energy. To address the high V loss and limited performance observed in solar cells utilizing fluorinated acceptors, we propose a strategy involving acceptor side-chain modifications. These results provide new insights into enhancing the performance of organic solar cells. [ABSTRACT FROM AUTHOR]

• Increasing donor side chain size leads to reduced CT dissociation efficiency. • Increasing acceptor side chain size results in reduced device voltage losses. • Highest PCE is realized when both the donor and acceptor are with large side chains. Increasing the size of the side chains of the donor or the acceptor materials is a highly effective strategy to reduce voltage losses, and increase the open-circuit voltage (Voc) of organic solar cells (OSCs). However, higher Voc does not necessarily translate to improved overall performance. To optimize side-chains and improve the performance of OSCs, the origin of the impact of the increased size of the donor and/or acceptor side side-chains size on the performance of OSCs is investigated. The study demonstrates that increasing the size of donor side chains can increase Voc, but it can also lead to deteriorated molecular packing, limiting overall solar cell performance. On the other hand, increasing the size of acceptor side chains can also increase Voc and improve molecular packing properties of the active layer, resulting in improved solar cell performance. Finally, the study shows that the best photovoltaic performance is achieved when both the donor and acceptor have large side chains. This research establishes the relationship between side chains of active materials, molecular packing properties, and the energetics of the donor/acceptor active layer, which is crucial for overcoming performance bottlenecks in OSCs. [ABSTRACT FROM AUTHOR]

A new nonfused ring electron acceptor PDI-DO-2F is designed and synthesized by attaching perylenediimide (PDI) unit as a pendent group to the central donor core. Compared with the control molecule DO-2F , the introduction of PDI lateral substituent can greatly enhance the solubility and decrease the crystallinity of the resulted acceptor. The PBDB-T :PDI-DO-2F blend film exhibits a much better morphology with higher and more balanced carrier mobility in contrast to PBDB-T :DO-2F one. PDI-DO-2F based organic solar cells (OSCs) give a power conversion efficiency (PCE) of 11.78%, higher than DO-2F based ones (9.82%). Furthermore, PDI-DO-2F based OSCs shows a Δ E non-rad value of 0.23 eV, which is significantly lower than the DO-2F based ones (0.28 eV). More importantly, the addition of PDI-DO-2F as the third component to the PBDB-T :DO-2F binary system can optimize the morphology of blend films and improve the shelf stability of devices. And the PBDB-T :DO-2F : PDI-DO-2F based ternary OSCs achieve a higher PCE of 13.82%. [Display omitted] • A new nonfused ring electron acceptor is designed and synthesized. • PDI unit as a pendent group can greatly enhance the solubility and decrease the crystallinity of the acceptor. • Significantly different power conversion efficiencies of 9.82%, 11.78% and 13.82% are achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three small molecular acceptors were designed and synthesized. • Noncovalent Conformational Locks and Side-Chain Engineering can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.09%, 12.30% and 14.25% are achieved. Three novel small molecular acceptors (SMAs) BO-2F , BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T: BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • We can modularly synthesize two fully nonfused ring acceptors with only four high-yield steps. • A simple fully nonfused ring electron acceptor can achieve a high PCE of over 12%. • The high FOM of 4T-OEH indicates its great potential for future practical applications. We designed two simple fully nonfused ring electron acceptors 4T-OEH and 4T-EH with 3,4-bis(alkoxy)thiophene and 3,4-dialkylthiophene π-bridge units, respectively, which can be modularly synthesized with only four high-yield steps. With the help of intramolecular S-O noncovalent interaction, 4T-OEH tends to form a planar molecular backbone, which is beneficial for the electron delocalization and charge transport. Besides, the neat 4T-OEH film displays a more ordered molecular packing and obviously red-shifted absorption after thermal annealing. Compared with 4T-EH , 4T-OEH based devices can form more homogenous phase morphology, higher and more balanced hole and electron mobilities. The optimal OSCs based on 4T-OEH can generate an excellent PCE of 12.12%, which is much higher than 4T-OEH based ones (7.36%). It is worth noting that the figure-of-merit values of 4T-OEH is much higher than the star acceptors (ITIC and Y6), demonstrating its high potential for future practical application. Our work has demonstrated that we can tune the backbone planarity, solubility and packing behavior of acceptor molecules via optimizing their lateral substituents to obtain high efficiency and low-cost fully nonfused ring electron acceptors. [ABSTRACT FROM AUTHOR]

• Minor terminal and central changes endow DO-2F and FO-N complementary absorption. • Asymmetrical FO-N effectively suppress the self-aggregation of DO-2F. • Acceptor alloy is found between the FO-N and DO-2F. • Alloy state acceptors produce suitable morphology with reduced V nr of 0.23 eV. • FO-N is an excellent third component for highly efficient OSCs of 14.10% Nonfused ring acceptors have shown great potential for future commercial applications of organic solar cells (OSCs) due to their simple structure and low synthetic costs. Herein, a novel asymmetrical nonfused ring acceptor FO-N with one branched lateral chain and one fluoro substituent at the central phenylene core was designed and introduced into PBDB-T : DO-2F binary system to fabricate high-efficiency ternary OSCs. The high-lying LUMO level of FO-N is conducive to improve V oc for ternary devices. More importantly, the introduction of FO-N as the third component can efficiently improve the compatibility of the ternary system via tuning the crystal size and optimizing the blend film morphology, which is beneficial to charge separation and reduced the non-radiative energy loss (Δ E nonrad). Finally, the ternary device achieved a low Δ E nonrad of 0.23 eV and a greatly improved PCE of 14.10% and with a V oc of 0.88 V, a J sc of 21.48 mA/cm2 and an FF of 74.41%. These results imply that the asymmetric nonfused ring acceptor design strategy is an effective way for optimizing the photovoltaic performance of highly crystallized blend system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two isomeric fully nonfused ring electron acceptors are designed and synthesized. • The location of diphenylamine units can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.83% and 0.43% are achieved. We have designed and synthesized two fully nonfused ring electron acceptors LW-in-2F and LW-out-2F with two diphenylamine side chains at different positions of the bithiophene core. The two diphenylamine side chains of LW-in-2F and LW-out-2F are at the outside and inside positions of the central bithiophene unit, respectively. The performance of LW-in-2F and LW-out-2F -based devices is very different, the photoelectric conversion efficiency (PCE) of LW-out-2F -based device is as high as 12.83%, while the efficiency of LW-in-2F -based device is only 0.43%. By GIWAXS test, we found that the change of diphenylamine position affects the way of molecular arrangement. When the diphenylamine side chain is located on the outer side of the central core, the molecular arrangement shows face-on orientation, which is beneficial for perpendicular charge transport, resulting in high and balanced charge mobilities and high PCE. [ABSTRACT FROM AUTHOR]