Morphology dependent electron transport in an n-type electron accepting small molecule for solar cell applications

Abstract

We report on the charge transport properties of a simple solution processable small-molecule electron acceptor, 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile (K12), designed for use in bulk-heterojunction organic photovoltaic cells. It was found that the molecular order in as-cast films can be dramatically improved by annealing at moderate temperatures (60 °C), which leads to a greatly enhanced electron mobility. Using the photoinduced charge extraction in linearly increasing voltage technique we measured bulk electron mobilities to be as high as 10−4 cm2 V−1 s−1, comparable with some of the best nonfullerene acceptor materials reported to date.

Advantage of suppressed non-Langevin recombination in low mobility organic solar cells

“…Nevertheless, the measured dark-CELIV transients show a "flat" response ( Fig. 2), 27,28 demonstrating the absence of equilibrium charge carriers, and hence the active layer of the solar cell is intrinsically undoped. Negligible doping allows simplified parameter estimation from the RPV technique 12 and is important for good device performance.…”

A flexible n-type organic semiconductor for optoelectronics

“…The asdeposited spin-coated films (230 nm thick) showed mobilities in the range 1.2-1.7 Â 10 À6 cm 2 V À1 s À1 . 16 The as-deposited evaporated films had mobilities in the range 3.4-3.7 Â 10 À6 cm 2 V À1 s À1 , which is on average marginally higher than the solution processed films. This is consistent with a slightly more structured film (as seen in Fig.…”

“…The detailed description of the Photo-CELIV experiment can be found elsewhere. 16 7-(9,9-Di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazole-4-carbaldehyde 3. A mixture of (9,9-di-n-propyl-9H-fluoren-2-yl)boronic acid (0.24 g, 0.82 mmol), 7-bromobenzo[c][1,2,5] thiadiazole-4-carbaldehyde (0.2 g, 0.82 mmol), tetrakis(triphenylphosphine)palladium(0) (29 mg, 0.02 mmol), t-butanol (1.21 cm 3 ), aqueous sodium carbonate (2 M, 1.2 cm 3 ), and toluene (3.6 cm 3 ) was deoxygenated by placement under vacuum at 400 mbar and back filling with argon four times and then heated at 85 C under argon for 17 h. After the mixture was allowed to cool to room temperature, the reaction was quenched with hydrochloric acid (2 M, 10 cm 3 ).…”

Recent advances of non-fullerene, small molecular acceptors for solution processed bulk heterojunction solar cells

“…This has been conrmed independently by measuring the inuence of annealing on as-cast K12 lms. 112,113 Moreover, the contribution of K12 to the produced photo-current could be explained either by energy transfer from the excited K12 to P3HT followed by electron transfer back to the acceptor (Channel I process) or by the photo-induced hole transfer (PHT) from K12 to P3HT (Channel II process). 110 Coupling the dicyanovinyl-benzothiadiazole with di-n-propylated dithienylsilole unit has led to a narrow band gap MA (YF25, Fig.…”