Solid Additive Delicately Controls Morphology Formation and Enables High‐Performance in Organic Solar Cells
Zhong LianZhe SunSeunglok LeeSeonghun JeongSungwoo JungYongjoon ChoJeewon ParkJaeyeong ParkSeong‐Jun YoonChangduk Yang
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Abstract Volatile solid additives are an effective strategy for optimizing morphology and improving the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Much research has been conducted to understand the role of solid additives in active layer morphology. However, it is crucial to delve deeper and understand how solid additives affect the entire morphology evolution process, from the solution state to the film state and the thermal annealing stage, which remains unclear. Herein, the use of a highly crystalline solid additive, phenoxathiin (Ph), in D18‐Cl:N3‐based OSCs and study its impact on morphology formation and photovoltaic performance is presented. Owing to its good miscibility with the acceptor N3, Ph additive can not only extend the time for the active layer to form from the solution state to the film state, but also provide sufficient time for acceptor aggregation. After thermal annealing, Ph solid additive volatilizes better aligned the N3 molecules and formed a favorable hybrid morphology. Consequently, the D18‐Cl:N3–based OSC exhibited an outstanding PCE of 18.47%, with an enhanced short‐circuit current of 27.50 mA cm −2 and a fill factor of 77.82%. This research is spurring the development of high‐performance OSCs using solid additives that allow fine control during morphology development.Keywords:
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Abstract Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6‐Tz20 by incorporating the 5,5′‐dithienyl‐2,2′‐bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6‐Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6‐Tz20: Y6‐based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance.
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The dependence of active-layer thickness on the power conversion efficiency (PCE) of inverted organic photovoltaics (OPVs) based on poly(3-hexylthiphene) and [6,6]-phenyl-C61-butyric acid methyl ester was investigated. When PCEs were measured immediately after device fabrication, the optimum thickness was ~100 nm. It was, however, found that thick OPVs exhibit higher PCEs a few months later, whereas thin OPVs simply degraded with time. Consequently, the optimum thickness changed with time. Considering this fact, we discuss the relationship between the active-layer thickness and PCE.
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In this paper, we investigated the optical performance of bulk heterojunction organic solar cells (OSCs) based on P3HT:PCBM (poly (3-hexylthiophene): phenyl-C61-butyric acid methyl ester) and PCPDTBT:PCBM (poly(2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta(2,1-b;3,4-b0)dithiophene)-alt-4,7-(2,1,3-benzothiadia-zole)):phenyl-C61-butyricacidmethylester). Light absorption and exciton generation rate were calculated in active layer. Short circuit current density was calculated as function of active layer thickness. Results of this model predict that OSCs based on PCPDTBT:PCBM have better performance than P3HT:PCBM based OSCs for active layer thickness more than 107nm.
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In recent years organic material based SCs (solar cells) has gained huge attention over traditional photovoltaics due to its low manufacturing cost, renewable feedstock, production scalability, light weight and mechanical flexibility. However the efficiency and durability of organic material based SCs need to be enhanced to make it commercially successful. Active layer material used in organic SC plays a significant role in determining its durability. P3HT:PCBM is the widely used active layer material. Various studies were carried out with different combination of active layer materials to enhance the performance of organic SCs. In this article we have studied the performance of organic SCs fabricated using two different active layer materials namely PCDTBT:PCBM and PTB7: PCBM
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Comprehensive Summary Organic solar cells (OSCs) present a promising renewable energy technology due to their cost‐effectiveness, adaptability, and lightweight nature. The advent of non‐fullerene acceptors has further boosted their significance, allowing for power conversion efficiencies surpassing 19% even with an active layer thickness of about 100 nm. However, in order to achieve large scale production, it is necessary to fabricate OSCs with thicker active layers exceeding 300 nm that are compatible with large‐area printing techniques. Nevertheless, OSCs with thick active layers have inferior performance compared to those with thin active layers. To expedite the transition of OSCs from laboratory to industrial high‐throughput manufacturing, considerable efforts have been made to comprehend the performance limitations of thick active‐layer OSCs, develop novel photoactive materials that are high‐performance and tolerant towards the thickness of the active layer, and optimize the morphology of the photoactive layer and device structure. This review aims to provide a comprehensive summary of the mechanisms that lead to efficiency loss in thick active‐layer OSCs, the representative works on molecular design, and the optimization strategies for high‐performance thick active‐layer OSCs, and the remaining challenges that must be addressed.
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In organic solar cells (OSCs), the morphology of the active layer plays a significant role in exciton dissociation into charge carriers and their subsequent transportation and extraction. The morphology of the active layer depends upon the thickness, concentration, and pre-post treatments. In this study, we investigated the effect of thickness on the morphology of the active layer and the resulting photovoltaic performance of semitransparent (ST) bulk heterojunction OSCs. We used a blend of PBDB-T (polymer donor) and a well-known nonfullerene small-molecule acceptor ITIC as the active layer for fabricating opaque (OP) and ST OSCs. This study is performed under ambient conditions. To obtain active layer films with thicknesses ranging from 350 to 100 nm, the rotations per minute (rpm) of the spin coating was varied from 1000 to 4000. Through a comprehensive analysis, we identified the optimal rpm for achieving an efficient active layer morphology and improved device performance for both OP and ST devices. We have achieved overall power conversion efficiencies of 10.39 and 7.26% for optimized OP and ST OSCs, respectively. The effect of varying the rpm of the active layer on nonradiative voltage loss is also studied. The correlation between the rpm, active layer morphology, and the overall performance of the ST OSCs is elucidated by our findings, providing valuable insights into optimizing devices. The results of this study could potentially aid in the development of more effective photovoltaic devices.
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Ternary blend active layers that include an additional electron donor or electron acceptor material provide the means to easily tune the transmission properties of semitransparent organic solar cells (OSCs) by simply changing the relative concentration of each active material. We added a nonfullerene acceptor (ITIC) into a well-studied donor:acceptor active layer (PCDTBT:PC71BM) that can be produced in air and demonstrates long-term operational stability. We investigated the optoelectronic properties of the resulting OSCs and observed that partially replacing the fullerene electron acceptor, PC71BM, with ITIC produces uniformly absorbing active layers, which, however, generate a slight decrease in photovoltaic performances compared to the reference binary OSCs. On the other hand, adding ITIC to an optimized PCDTBT:PC71BM ratio of 1:4 leads to a slight increase in short-circuit current density from these ternary OSCs with respect to the binary ones. In semitransparent OSCs fabricated with a PCDTBT:PC71BM:ITIC ratio of 1:4:1, power conversion efficiencies of 4%, average visible transparencies around 40% and color rendering indices of 97 are produced. As the addition of ITIC does not affect the long-term operational stability of the unencapsulated PCDTBT:PC71BM OSCs, our study opens the path to the fabrication of stable semitransparent OSCs with balanced optoelectronic properties that could readily be applied as solar energy-harvesting photovoltaic windows.
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Abstract Developing efficient organic solar cells (OSCs) with relatively thick active layer compatible with the roll to roll large area printing process is an inevitable requirement for the commercialization of this field. However, typical laboratory OSCs generally exhibit active layers with optimized thickness around 100 nm and very low thickness tolerance, which cannot be suitable for roll to roll process. In this work, high performance of thick‐film organic solar cells employing a nonfullerene acceptor F–2Cl and a polymer donor PM6 is demonstrated. High power conversion efficiencies (PCEs) of 13.80% in the inverted structure device and 12.83% in the conventional structure device are achieved under optimized conditions. PCE of 9.03% is obtained for the inverted device with active layer thickness of 500 nm. It is worth noting that the conventional structure device still maintains the PCE of over 10% when the film thickness of the active layer is 600 nm, which is the highest value for the NF‐OSCs with such a large active layer thickness. It is found that the performance difference between the thick active layer films based conventional and inverted devices is attributed to their different vertical phase separation in the active layers.
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