A non-fullerene, all-small-molecule solar cell (NF-SMSC) device uses the blend of a small molecule donor and a small molecule acceptor as the active layer. Aggregation ability is a key factor for this type of solar cell. Herein, we used the alkylthienyl unit to tune the aggregation ability of the diketopyrrolopyrrole (DPP)-based small molecule donors. Replacing two alkoxyl units in BDT-O-DPP with two alkylthienyl units yields BDT-T-DPP, and further introducing another two alkylthienyl units into the backbone produces BDT-T-2T-DPP. With the introduction of alkylthienyl, the backbone becomes twisted. As a result, the ππ-stacking strength, aggregation ability, and crystallite size all obey the sequence of BDT-O-DPP > BDT-T-DPP > BDT-T-2T-DPP. When selected a reported perylene diimide dimer of bis-PDI-T-EG as acceptor, the best NF-SMSC device exhibits a power conversion efficiency of 1.34, 2.01, and 1.62%, respectively, for the BDT-O-DPP, BDT-T-DPP, and BDT-T-2T-DPP based system. The BDT-T-DPP/bis-PDI-T-EG system yields the best efficiency of 2.01% among the three combinations. This is due to the moderate aggregation ability of BDT-T-DPP yields moderate phase size of 30–50 nm, whereas the strong aggregation ability of BDT-O-DPP gives a bigger size of 50–80 nm, and the weak aggregation ability of BDT-T-2T-DPP produces a smaller size of 10–30 nm. The BDT-T-DPP/bis-PDI-T-EG combination exhibits balanced hole/electron mobility of 0.022/0.016 cm2/(V s), whereas the BDT-O-DPP/bis-PDI-T-EG and the BDT-T-2T-DPP/bis-PDI-T-EG blend show a hole/electron mobility of 0.0011/0.0057 cm2/(V s) and 0.0016/0.11 cm2/(V s), respectively.Keywords: alkylthienyl position; all-small-molecule solar cell; donor backbone; non-fullerene; phase-separated nanostructure; solution-processed;

One of the key issues limiting the efficiency of non-fullerene organic solar cells (NF-SCs) is the low electron mobility and strong recombination loss. In this paper, we report an approach of fine-tuning the parameters relative to the film-forming kinetics to increase the power conversion efficiency, which significantly improved from 1.4 up to 6.1%. The film-forming process was judiciously optimized by carefully manipulating the following four parameters: the additive content during film processing, the volume of the host solvent for solvent vapor annealing (SVA), the volume ratio of the additive versus the host solvent for SVA, and the time for SVA. Through such controls, the photocurrent dramatically increased from 5.40 to 12.83 mA/cm2 and the fill factor from 32.61 to 56.43% as a result of the reduction of the monomolecular and bimolecular loss and the improvement of the electron mobility. These improvements in the electric properties are associated with the reconstruction of the film morphology, i.e., solvent annealing of the as-cast active film leads to the improvement of the phase segregation and the consequent enhancement of the self-aggregation of the blend donor and acceptor molecules in the solar cell active film.

Carrier mobility is a vital factor determining the electrical performance of organic solar cells. In this paper we report that a high-efficiency nonfullerene organic solar cell (NF-OSC) with a power conversion efficiency of 6.94 ± 0.27% was obtained by optimizing the hole and electron transportations via following judicious selection of polymer donor and engineering of film-morphology and cathode interlayers: (1) a combination of solvent annealing and solvent vapor annealing optimizes the film morphology and hence both hole and electron mobilities, leading to a trade-off of fill factor and short-circuit current density (Jsc); (2) the judicious selection of polymer donor affords a higher hole and electron mobility, giving a higher Jsc; and (3) engineering the cathode interlayer affords a higher electron mobility, which leads to a significant increase in electrical current generation and ultimately the power conversion efficiency (PCE).

A non-fullerene, all-small-molecule solar cell (NF-SMSC) device uses the blend of a small molecule donor and a small molecule acceptor as the active layer. Aggregation ability is a key factor for this type of solar cell. Herein, we used the alkylthienyl unit to tune the aggregation ability of the diketopyrrolopyrrole (DPP)-based small molecule donors. Replacing two alkoxyl units in BDT-O-DPP with two alkylthienyl units yields BDT-T-DPP, and further introducing another two alkylthienyl units into the backbone produces BDT-T-2T-DPP. With the introduction of alkylthienyl, the backbone becomes twisted. As a result, the ππ-stacking strength, aggregation ability, and crystallite size all obey the sequence of BDT-O-DPP > BDT-T-DPP > BDT-T-2T-DPP. When selected a reported perylene diimide dimer of bis-PDI-T-EG as acceptor, the best NF-SMSC device exhibits a power conversion efficiency of 1.34, 2.01, and 1.62%, respectively, for the BDT-O-DPP, BDT-T-DPP, and BDT-T-2T-DPP based system. The BDT-T-DPP/bis-PDI-T-EG system yields the best efficiency of 2.01% among the three combinations. This is due to the moderate aggregation ability of BDT-T-DPP yields moderate phase size of 30–50 nm, whereas the strong aggregation ability of BDT-O-DPP gives a bigger size of 50–80 nm, and the weak aggregation ability of BDT-T-2T-DPP produces a smaller size of 10–30 nm. The BDT-T-DPP/bis-PDI-T-EG combination exhibits balanced hole/electron mobility of 0.022/0.016 cm2/(V s), whereas the BDT-O-DPP/bis-PDI-T-EG and the BDT-T-2T-DPP/bis-PDI-T-EG blend show a hole/electron mobility of 0.0011/0.0057 cm2/(V s) and 0.0016/0.11 cm2/(V s), respectively.Keywords: alkylthienyl position; all-small-molecule solar cell; donor backbone; non-fullerene; phase-separated nanostructure; solution-processed;

One of the key issues limiting the efficiency of non-fullerene organic solar cells (NF-SCs) is the low electron mobility and strong recombination loss. In this paper, we report an approach of fine-tuning the parameters relative to the film-forming kinetics to increase the power conversion efficiency, which significantly improved from 1.4 up to 6.1%. The film-forming process was judiciously optimized by carefully manipulating the following four parameters: the additive content during film processing, the volume of the host solvent for solvent vapor annealing (SVA), the volume ratio of the additive versus the host solvent for SVA, and the time for SVA. Through such controls, the photocurrent dramatically increased from 5.40 to 12.83 mA/cm2 and the fill factor from 32.61 to 56.43% as a result of the reduction of the monomolecular and bimolecular loss and the improvement of the electron mobility. These improvements in the electric properties are associated with the reconstruction of the film morphology, i.e., solvent annealing of the as-cast active film leads to the improvement of the phase segregation and the consequent enhancement of the self-aggregation of the blend donor and acceptor molecules in the solar cell active film.