Nonhalogenated‐Solvent‐Processed High‐Performance All‐Polymer Solar Cell with Efficiency over 14%

Abstract

Rapid developments in material design have led to significant breakthroughs in the power conversion efficiency (PCE) of all‐polymer solar cells (all‐PSCs) in recent years. However, most of these devices are processed using halogenated solvents. Here, nonhalogenated solvent o‐xylene (o‐XY)‐processed all‐PSCs based on PBDB‐T:PJ1 are studied. Interestingly, it is found that the efficiency of the all‐PSCs can be greatly improved to 14.34% by simply increasing the spin‐coating speed during device processing. Careful studies reveal that this improvement could be attributed to the stronger centrifugal force (resulting from a higher spin‐coating speed), shorten the film formation time, and inhibit the excessive aggregation of PJ1. Consequently, a blend film with more reasonable domain size is formed. Based on these findings, another polymer acceptor PJ2, which bears a similar backbone to PJ1 but contains an additional thiophene spacer, is designed. PJ2 exhibits a much weaker aggregation ability and is used as a compatibilizer to improve the miscibility between the PBDB‐T and PJ1. Eventually, PBDB‐T:PJ1:PJ2‐based ternary all‐PSCs with a best PCE of 14.28% but processed under more mild conditions are obtained. These results may provide guidelines for future industrial fabrication of large‐area all‐PSCs.

π‐Extended Conjugated Polymer Acceptor Containing Thienylene–Vinylene–Thienylene Unit for High‐Performance Thick‐Film All‐Polymer Solar Cells with Superior Long‐Term Stability

“…Upon exciting the acceptor at their absorption peak (776 and 787 nm for PJTET and PJTVT respectively, Figure 5B), the calculated PL quenching efficiency is also higher for PJTVT in blend film than for PJTET (88.81% vs 85.06%). Overall, in comparison to TET, PL results indicate that the incorporation of TVT linkage on the backbone could lead to a more closely D/A interface contact for more efficient charge separation and transport, [ 22,42 ] which is consistent with the improved J SC value in devices.…”

“…The χ donor:acceptor acquired through the Flory−Huggins model provides a critical evaluation index for donor:acceptor miscibility. [ 22,36 ] Generally, the χ is related to the propensity of phase segregation, for which a lower value represents favorable miscibility, whereas a higher value indicates phase separation. [ 22 ] As a result, the χ JD40:PJTVT (0.01 K) is relatively less than χ JD40:PJTET (0.05 K), which demonstrates better miscibility between JD40 and PJTVT instead of PJTET, leading to a reduced domain size for JD40:PJTVT that is consistent with the results of TEM.…”

“…This provides an alternative strategy to optimize the properties of the PSMAs to maximize the efficiency of all‐PSCs. [ 10,13,15,22 ] However, the effect of conjugation of linkage unit on the properties of PSMAs is not well contrastively studied in previous works as far as we know, and whether the linkage unit should be conjugated or not is not well demonstrated. Moreover, P A s with high efficiency, good stability, and thickness‐insensitivity, which are favorable for the practical application of all‐PSCs, are still rarely seen in literature.…”

“…[ 10,20 ] While some studies demonstrated that the selection and modification of linkage units should also be taken into consideration to tune the properties of PSMAs. For example, some recent works concentrated on that by using linkage units, like thiophene, [ 10,21 ] bithiophene, [ 22 ] benzodithiophene, [ 13 ] and nonconjugated or non‐fully conjugated unit, [ 23,24 ] the regulation on these linkage units can remarkably affect the optical and electronic properties of resulting polymers. This provides an alternative strategy to optimize the properties of the PSMAs to maximize the efficiency of all‐PSCs.…”

Hot‐Casting Boosts Efficiency of Halogen‐Free Solvent Processed Non‐Fullerene Organic Solar Cells

“…Motivated by the above considerations, a number of works have focused on molecular structure modification of organic photovoltaic materials to regulate their solubility, film morphology, and photovoltaic performance using halogen‐free solvents. [ 16,17,25–27 ] For instance, the optimized alkyl chain length of polymer donor PffBT4T‐C 9 C 13 endows it excellent solubility in 1,2,4‐trimethylbenzene (TMB), and film processed from warm TMB exhibits reduced domain sizes and better face‐on molecular orientation, thus yields a higher PCE than the halogenated solvent processed counterpart. [ 28 ] In a similar way, a well‐known non‐fullerene acceptor (NFA) Y6's ethylhexyl side chains were substituted by longer butyloctyl chains to enhance its processability and photovoltaic performance by processing from halogen‐free solvents.…”