Bing Guo

High-efficiency small-molecule-based organic photovoltaics (SM-OPVs) using two electron donors (p-DTS(FBTTh₂)₂ and ZnP) with distinctively different absorption and structural features are reported. Such a combination works well and synergically improves device short-circuit current density (J_sc) to 17.99 mA cm⁻² and fill factor (FF) to 77.19%, yielding a milestone efficiency of 11%. To the best of our knowledge, this is the highest power conversion efficiency reported for SM-OPVs to date and the first time to combine high J_sc over 17 mA cm⁻² and high FF over 77% into one SM-OPV. The strategy of using multicomponent materials, with a selecting role of balancing varied electronic and structural necessities can be an important route to further developing higher performance devices. This development is important, which broadens the dimension and versatility of existing materials without much chemistry input.

High-efficiency all-small-molecule organic solar cells using two electron donors with distinctively different absorption and structural features are reported. Such a combination works well and synergically improves device current and fill factor, yielding a milestone efficiency of 10.97%.

Due to the short diffusion length of approximately 10 nm of an exciton in bulk heterojunction (BHJ) organic solar cells (OSCs) comprising electron donors and acceptors, a formation with well phase-separated nanomorphology in BHJ films has been one of the most important issues in achieving efficient charge separation and extraction in OSCs. By adding a small amount of a high boiling point solvent or molecules to a bulk heterojunction (BHJ) solution, processing additive techniques have recently begun to offer an attractive and efficient method for controlling the nanoscale BHJ morphology of state-of-the-art OSCs with power conversion efficiencies (PCEs) exceeding approximately 11%. However, it remains unknown whether the effect of processing additives can potentially pave the way for the ongoing development of various BHJ components and the commercialization of OSCs. Here, recent progress in understanding and developing the effects of processing additives on OSCs is highlighted. This overview suggests possible guidelines for a wide range of BHJ components with respect to morphological/structural evolution. Furthermore, the rational correlations among processing additives, BHJ components, and fabrication technologies and the performance of high-performance and low-cost OSCs are discussed along with future commercialization prospects.

For efficient charge separation and extraction in a device, the specific characteristics of processing additives, such as high boiling points and selective solubility, provide a special opportunity to form a well phase-separated nanomorphology in a bulk-heterojunction (BHJ) film. The applications of processing additives to commercial OPVs can be further developed with respect to future demands for various BHJ materials, such as high performance, long-term stability and eco-friendly fabrication.

The chemical structure of conjugated polymers plays an important role in determining their physical properties that, in turn, dictates their performance in photovoltaic devices. 5-Fluoro-2,1,3-benzothiadiazole, an asymmetric unit, is incorporated into a thiophene-based polymer backbone to generate a hole conducting polymers with controlled regioregularity. A high dipole moment is seen in regioregular polymers, which have a tighter interchain stacking that promotes the formation of a morphology in bulk heterojunction blends with improved power conversion efficiencies. Aliphatic side chain substitution is systematically varied to understand the influence of side chain length and symmetry on the morphology and resultant performance. This side chain modification is found to influence crystal orientation and the phase separated morphology. Using the asymmetric side chain substitution with regioregularity of the main chain, an optimized power conversion efficiency of 9.06% is achieved, with an open circuit voltage of 0.72 V, a short circuit current of 19.63 mA cm⁻², and a fill factor over 65%. These results demonstrate that the local chemical environment can dramatically influence the physical properties of the resultant material.

The unidirectional regioregular conjugated polymers using 5-fluoro-2,1,3-benzothiadiazole (FBT) asymmetric unit were synthesized. Compared with the regiorandom control polymers, the regioregular polymers with a unidirectional fluorine atom alignment can lead to a progressive dipole moment along the backbone. The regioregular FBT polymers exhibit tighter interchain stacking and better morphology in bulk heterojunction blends, giving rise to improved power conversion efficiency.

Narrow bandgap (1.37–1.46 eV) polymers incorporating a head-to-head linkage containing 3-alkoxy-3′-alkyl-2,2′-bithiophene are synthesized. The head-to-head linkage enables polymers with sufficient solubility and the noncovalent sulfur–oxygen interaction affords polymers with high degree of backbone planarity and film ordering. When integrated into polymer solar cells, the polymers show a promising power conversion efficiency approaching 10%.

A novel naphtho[1,2-c:5,6-c′]bis([1,2,5]­thiadiazole)-based narrow-bandgap π-conjugated polymer is designed for application in polymer solar cells. Remarkable power conversion efficiencies over 10% can be achieved based on both conventional and inverted device architectures with thick photoactive layers, which are processed by using chlorinated or nonhalogenated solvents, suggesting its great promise toward practical applications based on high-throughput roll-to-roll processing.

A ternary-blend strategy is presented to surmount the shortcomings of both fullerene derivatives and nonfullerene small molecules as acceptors for the first time. The optimal ternary device shows a high power conversion efficiency (PCE) of 10.4%. Moreover, a significant enhancement in PCE (≈35%) relative to both of the binary reference devices, which has never been achieved before in high-efficiency ternary devices, is demonstrated.

A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.