Yasunari Tamai

Singlet exciton diffusion plays a central role in the photovoltaic conversion in organic photovoltaics (OPVs). Upon light absorption, singlet excitons are promptly generated in organic materials instead of charge carriers because the dielectric constant (εr) is small (∼3-4), which is in sharp contrast to inorganic and perovskite solar cells. In order to convert to charge carriers, excitons need to diffuse into an interface between electron donor and acceptor materials before deactivating to the

Rapid, long-range charge separation in polymer-fullerene organic solar cells (OSCs) enables electrons and holes to move beyond their Coulomb capture radius and overcome geminate recombination. Understanding the nature of charge generation and recombination mechanisms in efficient, nonfullerene-acceptor-based OSCs are critical to further improve device performance. Here we report charge dynamics in an OSC using a perylene diimide (PDI) dimer acceptor. We use transient absorption spectroscopy to t

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExperimental study of the relation between contact angle and surface roughnessY. Tamai and K. ArataniCite this: J. Phys. Chem. 1972, 76, 22, 3267–3271Publication Date (Print):October 1, 1972Publication History Published online1 May 2002Published inissue 1 October 1972https://pubs.acs.org/doi/10.1021/j100666a026https://doi.org/10.1021/j100666a026research-articleACS PublicationsRequest reuse permissionsArticle Views1431Altmetric-Citations86LEARN ABOUT TH

Singlet exciton dynamics in crystalline domains of regioregular poly(3-hexylthiophene) (P3HT) films was studied by transient absorption spectroscopy. Upon the selective excitation of crystalline P3HT at the absorption edge, no red shift of the singlet exciton band was observed with an elapse of time, suggesting singlet exciton dynamics in relatively homogeneous P3HT crystalline domains without downhill relaxation in the energetic disorder. Even under such selective excitation conditions, the ann

Abstract Transient absorption spectroscopy (TAS) is a time‐resolved spectroscopic technique that can quantitatively observe temporal changes in the absorption spectrum associated with transient species, such as excitons and charges. Therefore, it is extensively used in photophysics, photochemistry, and photobiology. TAS plays a crucial role in unveiling charge generation and recombination dynamics in organic solar cells (OSCs). However, the interpretation of TA data is sometimes difficult for th

The mechanism of light‐induced degradation in organic solar cells based on regioregular poly(3‐hexylthiophene) and indene‐C 60 bisadduct is studied by transient absorption (TA) and electron spin resonance (ESR) measurements. After 45 h light exposure under simulated solar illumination at 100 mW cm −2 , the short‐circuit current density, open‐circuit voltage, and fill factor are all degraded by about 20%–30% relative to the initial photovoltaic parameters. For the assignment of limiting conversio

The voltage loss incurred by nonradiative charge recombination should be reduced to further improve the power conversion efficiency of organic solar cells (OSCs). This work discusses the nonradiative voltage loss in OSCs with systematically controlled energy offset between optical bandgap and charge transfer (CT) states. It is demonstrated that the nonradiative voltage loss is a function of the energy offset; it drops sharply with decreasing energy offset. By measuring the quantum yields of elec

Charge generation and recombination dynamics in a blend film of a crystalline low-bandgap polymer, poly[(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were studied by transient absorption spectroscopy. Upon photoexcitation of the PSBTBT absorption band at 800 nm, singlet excitons were promptly generated, and then rapidly converted into polarons in a few picosec

Abstract The power conversion efficiencies of organic solar cells (OSCs) have routinely lagged far behind those of their inorganic counterparts. However, owing to the enormous contributions of many researchers, the power conversion efficiencies of OSCs have rapidly improved and now exceed 19%. The charge generation mechanisms in OSCs have been heavily debated during this period while acquiring valuable knowledge. This review highlights fundamental and cutting‐edge research that rationalizes why

Suppression of nongeminate recombination due to long charge lifetime and low nonradiative loss is essential to highly efficient organic photovoltaics.

The dynamics of singlet fission in poly(9,9′-di-n-octylfluorene) (PFO) films was studied by transient absorption spectroscopy. Under a high excitation intensity, triplet excitons were rapidly interconverted from singlet excitons on a picosecond time stage. From the excitation intensity dependence of the generation yield, the rapid triplet exciton formation is attributed to the singlet fission from a higher singlet excited state Sn formed by the singlet–singlet annihilation (singlet fusion follow

Effect of aromaticity on triplet exciton dynamics was studied by transient absorption spectroscopy for two fluorene-based random copolymers with different aromatic amine, poly(9,9′-di-n-octylfluorene-ran-N,N′-bis(4-n-butylphenyl)-N,N′-diphenyl-1,4-benzenediamine) (F8-PDA) and poly(9,9′-di-n-octylfluorene-ran-N,N′-bis(4-t-butylphenyl)-N,N′-diphenyl-9,10-anthracenediamine) (F8-ADA). On a time scale of nanoseconds, triplet exciton was efficiently formed in F8-PDA through the intersystem crossing (I

In this paper, we introduce a new strategy for improving the efficiency of upconversion emissions based on triplet-triplet exciton annihilation (TTA-UC) in the solid state. We designed a ternary blend system consisting of a triplet sensitizer (TS), an exciton-transporting host polymer, and a small amount of an annihilator in which the triplet-state energies of the TS, host, and annihilator decrease in this order. The key idea underpinning this concept involves first transferring the triplet exci