Efficient full-small molecule organic solar cell

Since the development of organic semiconductor devices and the manufacturing process, organic solar cells have made great progress. However, from small molecules and small molecule receptor donor whole small molecule organic solar cells (SM-OSCs) is much lower than the efficiency of a polymer composed of a body, a small molecule receptor polymer solar cells (of PSCs) efficiency thereof. Since the polymer having a donor PSCs length between the molecular skeleton and strong intermolecular forces, structured polymer film itself can form an interpenetrating polymer network suitable for the PSCs. Accordingly, when blended with small molecule receptor, it is easy to meet PSCs suitable phase separation, and therefore, without any post-treatment of most PSCs can provide reasonably efficient photovoltaic performance. However, for the SM-OSCs, since the chemical structures and physical chemistry of small molecules and small molecule acceptor donor material similar nature, it is difficult to achieve proper phase separation. Thus, although the SM-OSCs film having high charge mobility, but it is always relatively low Jsc and FF. In order to improve the photovoltaic performance of SM-OSCs, for a – is a very important receptor mixing the active layer nanotopography fine adjustment. Morphology of the active layer common way regulation are: physical methods like solvent additive solvent vapor annealing, thermal annealing; modification of a structure in the organic semiconductor material, such as engineering side chain, a fluorine atom, isomerization chemically, are aggregation and accumulation can regulate the molecular morphology, thus affecting the bulk heterojunction solar cell (a BHJ) morphology and photovoltaic performance. the Institute of Chemistry / Suzhou University Li Yongfang Academy , Meng Lei researcher, joint Zhejiang University Professor Zhu Haiming al Based thiophene conjugated different side chain substituent starting synthesized small molecule to molecule to two kinds of materials, including an alkylthio SM1-S SM1-F and a fluoroalkyl group having a substituent, and substituted with an alkyl group as previously reported SM1, the influence of different side chains conjugated to a molecule to aggregate and photophysical, photovoltaic characteristics. The results showed that the receptor Y6 is, 120 deg.] C for 10 minutes thermal anneal SM1-F group the SM-OSCs The power conversion efficiency (PCE) up to 14.07% , is reported most SM-OSCs one good value. Furthermore, these results also show that crystallization and aggregation characteristics of different characteristic side chain thereof Small MoleculesHave a significant impact, thermal annealing treatment is effective to fine-tune the phase separation to form a suitable acceptor interpenetrating network, which facilitates exciton dissociation and charge transport, resulting in efficient photovoltaic performance. to the article entitled \”Adoption of the donor side chain engineering, thermal annealing process for preparing high-performance all-small molecule organic solar cells\” published in leading journals on international material \”advanced materials,\” corresponding author for the Institute of Chemistry Lee Wing-fang academician , Meng Lei, a researcher .

[Photo Analysis]

Researchers have different substituents on the side chain conjugated thiophene, comprising SM1-S alkylthio with fluorine and with Effects of the side chains of molecular aggregates as well as for photovoltaic and photophysical properties of the molecule and alkyl substituents SM1-F, and a donor molecule having alkyl substituents SM1 previously reported for different studies conjugate . FIG. 1 is a structural material molecular structure, fabricating a device, the optical properties of the new composite material, and a band diagram.

As shown in FIG. 2, the thermal annealing device performance improved significantly after the treatment, the optimum value of PCE device SM1-F group up to 14.07%, Voc values ​​up to 0.866V, Jsc value 23.25mA cm [123 ] -2 ^{, FF value is 0.699, and the SM1-F-based mixed film device having a film thickness of 250 nm further efficiency of 11.9%, indicating the potential for a large area of ​​the prepared SM-OSCs,} due to SM1- F: hole mobility higher Y6 mixing the active layer and the balance with the hole and electron mobility, bimolecular complex weak.

FIG. 2: a) based on the J-V characteristic curves SM1, SM1-S and SM1-F optimization SM-OSCs is (at 120 deg.] C treated TA 10 minutes). b) IPCE curve corresponds to SM-OSCs. c) presence or absence of small molecule heat back donorHole mobility after the fire treatment. d) SM-OSCs strong dependence of the light VOC. e) SM-OSCs strong dependence of the light Jsc. f) the small molecule and the donor film Y6 blend charge carrier mobility in the presence or absence of the thermal annealing process.as shown in Figure 3-4, after the thermal annealing process, the film distribution Y6 no significant change, but slightly increased aggregation, the aggregation of small molecules to the film significantly enhanced. Compared with SM1 SM1-S and pure film, SM1-F film has more thermal annealing process and aggregated denser aggregation, which also shows different small molecule conjugated side chain donor to donor small molecule the gathering has a profound impact.

FIG. 3: a, b) TEM image of the pure film (scale bar = 500 nm): i) SM1 film, ii) SM1-S membrane, iii) SM1-F film, iv) Y6 film: a) non-annealed film, b) 10 minutes after thermal annealing of the film at 120 ℃.

FIG. 4: a, b) TEM image of the mixed film (scale bar = 500 nm): i) SM1: Y6 mixed film, ii) SM1-S: Y6 mixed film, iii) SM1-F: Y6 mixed film: a) non-annealed films, and b) 10 minutes at 120 deg.] C film by thermal annealing process. As shown inFIG. 5, the thermal annealing treatment is effective to facilitate phase separation of all small molecule blend. 3 illustrates a side chain in conjunction with engineering and thermal annealing process can effectively regulate the molecular aggregation and phase separation.

FIG. 5: a, b) AFM image of the mixed film and PiFM: a) SM1-F: Y6 cast, b) SM1-F: Y6 by thermal annealing process 120 ℃ 10min. i) AFM topography image corresponding mixed film. ii) an atomic force microscope image of the corresponding phase of the mixed film. iii-v) PiFM image corresponding mixed film: iii) based on the peak (SM1-F component), iv) 1715cm-1 based on the peak at (Y6 component) 1291cm-1 at, v) an image (iii) and (iv) to provide a combination of chemical SM1-F and Y6 of FIG.As shown in FIG 6 further study using transient absorption SM1-F: hole-Y6 blend filmsTransport kinetics, and improve the morphology as described exciton diffusion distance after extended thermal annealing process, the hole mobility is increased more than twice the mixed film, which is consistent with the significantly enhanced Jsc and the PCE in the SM-OSC .

FIG. 6: a) pure and Y6 SM1-F: TRPL spectrum Y6 blend films. b) as-cast the SM1-F: color spectrum of a transient absorption Y6 blend films. c) thermal annealing process SM1-F: color spectrum of a transient absorption Y6 blend films. d) the transient absorption spectra indicate the delay time. Transient relatively pure SM1-F film (gray dashed lines) and pure Y6 film (black dashed line) absorption spectrum. e) thermal annealing process SM1-F: Y6 blend films exhibit the hole transferring process SM1-F Y6 and transient absorption kinetics. f) Have the thermal annealing process SM1-f: the hole transfer process Y6 blend films. Gray curve represents the response Y6 neat film.

Conclusion Researchers have synthesized a series of wide-gap different substituents with a small molecular thiophene-donor conjugate on a side chain. In all of Y6 receptor SM-OSCs exhibited good photovoltaic performance. Wherein, based on the SM1-F SM-OSCs have a

up to 14.07% of the PCE , is one of the best efficiency of the SM-OSCs reported so far , which is preferably FF 0.699, higher Voc of 0.866 V. Further, based on the device SM1-F also has good thickness insensitivity, shows great potential for producing large area SM-OSCs. Morphological analysis showed that the small molecules of different side chain donor has a significant impact on its crystalline characteristics and aggregation characteristics. In addition, the thermal annealing treatment is effective to fine-tune the phase separation to form a suitable acceptor interpenetrating network resulted from efficient solutions excitons and charge transport, resulting in efficient SM-OSCs. This work not only to achieve efficient SM-OSCs, and a clear understanding of the effects of thermal annealing treatment and the side chains of engineering nanotopography, photophysical properties and photovoltaic performance of a photovoltaic material to provide for the further development and optimization of device SM-OSCs a guiding role. Reference Beibei Qiu et al. HighlyEfficient All-Small-Molecule OrganicSolar Cells with Appropriate Active Layer Morphology by Side Chain Engineering of Donor Molecules and Thermal Annealing, AM, 2020 DOI:. 10.1002 / adma.201908373.https: //doi.org/10.1002/adma.201908373