Solution-Processed Organic Solar Cells with High Open-Circuit Voltage of 1.3 V and Low Non-Radiative Voltage Loss of 0.16 V

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔV_non-rad) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (V_oc). Herein, OSCs are fabricated by adopting two pairs of D–π–A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (E_CT) as high as 1.70–1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔE_CT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10⁻³ and 1.0 × 10⁻³ are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔV_non-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high V_oc of 1.3 V. The ΔV_non-rad of 0.16 V and V_oc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.     

Doped/Undoped A1-A2 Typed Copolymers as ETLs for Highly Efficient Organic Solar Cells

The electron transport layer (ETL) is a critical component in achieving high device performance and stability in organic solar cells. Conjugated polyelectrolytes (CPEs) have become an attractive alternative due to film-forming properties and ease of preparation. However, p-type CPEs generally exhibit poor charge mobility and conductivity, incorporation of electron-withdrawing units forming alternated D-A conjugated backbone can make up for these deficiencies. Herein, the ratio of electron withdrawing moieties are further increased and two poly(A1-alt-A2) typed PIIDNDI-Br and PDPPNDI-Br based on the combination of naphthalene diimide (NDI) with isoindigo (IID) or diketopyrrolopyrrole (DPP) via direct arylation polycondensation are synthesized. These CPEs possess excellent alcohol solubility, a suitable lowest unocuppied molecular orbital energy level, and work function tunability. Surprisingly, the incorporation of IID and DPP units generate distinct self-doping behaviors, which are confirmed by UV–vis absorption and ESR spectra. However, no matter doped or undoped, both CPEs present better charge-transporting properties and conductivity when utilized as ETLs. The PIIDNDI-Br and PDPPNDI-Br display good universal compatibility with the blend of PM6:Y6 and PM6:L8-BO, and PCEs of 18.32% and 18.36% are obtained, respectively, which also present excellent storage stability. In short, the combination of two different acceptors demonstrates an efficient strategy to design highly efficient ETLs for high performance photovoltaic devices.     

Hybrid Perovskite Quantum Dot/Non-Fullerene Molecule Solar Cells with Efficiency Over 15%

Organic-inorganic hybrid film using conjugated materials and quantum dots (QDs) are of great interest for solution-processed optoelectronic devices, including photovoltaics (PVs). However, it is still challenging to fabricate conductive hybrid films to maximize their PV performance. Herein, for the first time, superior PV performance of hybrid solar cells consisting of CsPbI₃ perovskite QDs and Y6 series non-fullerene molecules is demonstrated and further highlights their importance on hybrid device design. In specific, a hybrid active layer is developed using CsPbI₃ QDs and non-fullerene molecules, enabling a type-II energy alignment for efficient charge transfer and extraction. Additionally, the non-fullerene molecules can well passivate the QDs, reducing surface defects and energetic disorder. The champion CsPbI₃ QD/Y6-F hybrid device has a record-high efficiency of 15.05% for QD/organic hybrid PV devices, paving a new way to construct solution-processable hybrid film for efficient optoelectronic devices.     

Recent advances and prospects of asymmetric non-fullerene small molecule acceptors for polymer solar cells

Recently,polymer solar cells developed very fast due to the application of non-fullerence acceptors.Substituting asym-metric small molecules for symmetric small molecule acceptors in the photoactive layer is a strategy to improve the perform-ance of polymer solar cells.The asymmetric design of the molecule is very beneficial for exciton dissociation and charge trans-port and will also fine-tune the molecular energy level to adjust the open-circuit voltage (Voc) further.The influence on the ab-sorption range and absorption intensity will cause the short-circuit current density (Jsc) to change,resulting in higher device per-formance.The effect on molecular aggregation and molecular stacking of asymmetric structures can directly change the micro-scopic morphology,phase separation size,and the active layer's crystallinity.Very recently,thanks to the ingenious design of act-ive layer materials and the optimization of devices,asymmetric non-fullerene polymer solar cells (A-NF-PSCs) have achieved re-markable development.In this review,we have summarized the latest developments in asymmetric small molecule acceptors(A-NF-SMAs) with the acceptor-donor-acceptor (A-D-A) and/or acceptor-donor-acceptor-donor-acceptor (A-D-A-D-A) struc-tures,and the advantages of asymmetric small molecules are explored from the aspects of charge transport,molecular energy level and active layer accumulation morphology.     

Non-fullerene acceptors based on multiple non-covalent interactions for low cost and air stable organic solar cells

Significant progresses have been made on organic solar cells (OSCs) in last few years, but the industrialization of OSCs is still hindered by high cost and poor device stability. Recently, the most successful OSCs are usually based on fused-ring small molecule non-fullerene acceptors (SM-NFAs) which often involve multiple complex synthetic steps and result in low overall yields and high cost. Herein, two easily accessible non-fused NFAs based on BT, CPDT and IC with different halogen atoms named BT-F and BT-Cl were designed and synthesized. Non-covalent interactions or conformation locks between BT and adjacent CPDT units provided planar conformations, which is beneficial for molecular packing and charge transport. When blended with low cost polymer donor PTQ-10, optimal devices based on BT-F provided a PCE of 8.26%. A higher PCE of 8.65% was obtained from BT-Cl-based devices. Low voltage loss of 0.57 and 0.59 V were observed for BT-F- and BT-Cl-based devices. It is noteworthy that devices based on PTQ-10:BT-F and PTQ-10:BT-Cl exhibited excellent stabilities when stored in ambient atmosphere for 10 days without encapsulation. This work demonstrates an example of pursuing low cost OSCs with excellent air stability.     

Stability Of Non-Fullerene Electron Acceptors and Their Photovoltaic Devices

Non-fullerene electron acceptors (NFAs) are recognized as “rising star” in recent years in the organic solar cells (OSCs) community. In contrast to the traditional fullerene electron acceptors, NFAs promise superior feasibility in molecular design with tunable optoelectronic properties, experiencing unprecedented development in the last 5 years with maximum achievable power conversion efficiencies over 18% are acquired in NFA based OSCs. Nevertheless, the stability of NFAs and their OSCs is still problematic and not well understood, and is regarded as the bottleneck toward the commercialization of NFA based OSCs. In this review, recent advances and current understanding of the stability of NFAs and their corresponding OSCs are presented. Specifically, three key factors, including chemical-, photon-, and thermal-, induced degradations in NFAs are analyzed and summarized, with approaches to enhance the stability suggested. This is followed by the discussion of shelf and operational stability of NFA based OSCs, with highlights of operational stabilities in inert, ambient, indoor, and outdoor conditions. It is envisaged that operational lifetime of over 20 years in real world is achievable via the joint efforts from material design, morphology control, interfacial engineering, and encapsulation technology.     

高效率有机太阳电池的理论建模

采用综合考虑温度、电场强度、载流子浓度的普遍迁移率模型,利用实际太阳能光谱和非富勒烯材料的吸收系数来计算载流子的产生,结合漂移扩散方程、电流连续性方程等对高效率有机太阳电池进行理论建模。利用该模型计算了器件的电流-电压曲线、开路电压-光照强度曲线和短路电流-光照强度曲线。结果发现,利用该模型计算的电流-电压曲线与实验数据符合很好,其他两种曲线也与实验数据符合较好。此外,利用该模型分析了能量无序度对器件性能的影响,结果表明减小材料的能量无序度可以提高有机太阳电池的性能。     

Effect of Cyano Substitution on Non-Fullerene Acceptor for Near-Infrared Organic Photodetectors above 1000 nm

Near-infrared organic photodetectors (NIR OPDs) comprising ultra-narrow bandgap non-fullerene acceptors (NFA, over 1000 nm) typically exhibit high dark current density under applied reverse bias. Therefore, suppression of dark current density is crucial to achieve high-performance of such NIR OPDs. Herein, cyano (CN) with a strong electron-withdrawing property is introduced into alkoxy thiophene as a π-bridge to adjust its optoelectronic characteristics, and the correlation between dark current density and charge injection barrier is investigated. Compared with their motivated NFA (COTH), the novel CN-substituted NFAs, COTCN and COTCN2, exhibited deeper-lying highest occupied molecular orbital energy levels and narrower optical bandgap (<1.10 eV), owing to the strong inductive and resonance effect of CN. The dark current and total noise currents are minimized as the number of substituted CN increases because of the larger hole injection barrier. Consequently, PTB7-Th:COTCN2 exhibited the best shot-noise limited detectivity (D^*_sh, 1.18 × 10¹² Jones) and total noise detectivity (D^*_n, 1.33 × 10¹¹ Jones) compared with those of PTB7-Th:COTH (D^*_sh, 2.47 × 10¹¹ Jones and D^*_n, 1.96 × 10¹⁰ Jones).     

Selective Chemical Reactivity of Non-Fullerene Acceptor for Photoelectrochemical Bioassay of Urease Activity

Non-fullerene acceptors (NFAs) are a crucial component of organic photovoltaics, and they have gained significant attention due to their outstanding photoelectric conversion efficiency. However, the recognition reactions of specific building blocks in NFAs are largely overlooked in the construction of photoelectrochemical (PEC) biosensing platforms. In this study, the potential of Y6, a prototype NFA, is explored to construct a sensitive PEC biosensor for monitoring urease activity due to the selective chemical reactivity of its organic building blocks. The resultant biosensor relies on the urease-mediated enzymatic reaction, which produces OH⁻ anions that act as a nucleophilic reagent for the linkage of C═C in the Y6 moiety. This results in the formation of Y6-OH, which exhibits a depressive photoelectric response due to the destroyed conjugated structure and intramolecular charge transfer. As expected, a linear relationship is observed between the recession of photoelectric performance and the concentration of urease, with good sensitivity and selectivity. Furthermore, urease activity detection is also successfully realized in human saliva samples, suggesting the promising potential of NFA-based PEC biosensors for clinical applications even in the absence of common biological recognition units.     

Asymmetric and Halogenated Fused-Ring Electron Acceptor for Efficient Organic Solar Cells

Fused-ring non-fullerene electron acceptors (NFAs) boost the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Asymmetric and halogenated NFAs have drawn increasing attention in recent years due to their unique optoelectronic properties. Starting from the symmetric NFA ITCC-M, this work systematically designs and synthesizes an asymmetric counterpart ITCC-M-2F, halogenated counterpart ITCC-Cl, and asymmetric and halogenated counterpart IDTT-Cl-2F. Among these NFAs, IDTT-Cl-2F shows the shallowest lowest unoccupied molecular orbital energy level, broader absorption range, and the tightest molecular packing. As a result, when blended with the donor PBDB-T-2Cl, IDTT-Cl-2F-based OSCs yield the highest PCE of 13.3% with an open-circuit voltage of 0.96 V, short-circuit current of 19.20 mA cm^–2, and fill factor of 71.1%, which is the highest PCE of OSCs employing 2-(2-chloro-6-oxo-5,6-dihydro-4H-cyclopenta[b]thiophen-4-ylidene) malononitrile (ClIC) unit terminated NFA. The results demonstrate the synergistic effect of asymmetry and halogenation toward tuning of the optoelectronic properties of NFAs for high performance OSCs.