Utilizing Energy Transfer in Binary and Ternary Bulk Heterojunction Organic Solar Cells

Abstract

Energy transfer has been identified as an important process in ternary organic solar cells. Here, we develop kinetic Monte Carlo (KMC) models to assess the impact of energy transfer in ternary and binary bulk heterojunction systems. We used fluorescence and absorption spectroscopy to determine the energy disorder and Förster radii for poly(3-hexylthiophene-2,5-diyl), [6,6]-phenyl-C61-butyric acid methyl ester, 4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (DIBSq), and poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-dihydrodithieno[3,2-c:3',2'-h][1,5]naphthyridine-5,10-dione). Heterogeneous energy transfer is found to be crucial in the exciton dissociation process of both binary and ternary organic semiconductor systems. Circumstances favoring energy transfer across interfaces allow relaxation of the electronic energy level requirements, meaning that a cascade structure is not required for efficient ternary organic solar cells. We explain how energy transfer can be exploited to eliminate additional energy losses in ternary bulk heterojunction solar cells, thus increasing their open-circuit voltage without loss in short-circuit current. In particular, we show that it is important that the DIBSq is located at the electron donor-acceptor interface; otherwise charge carriers will be trapped in the DIBSq domain or excitons in the DIBSq domains will not be able to dissociate efficiently at an interface. KMC modeling shows that only small amounts of DIBSq (<5% by weight) are needed to achieve substantial performance improvements due to long-range energy transfer.

Engineering Two-Phase and Three-Phase Microstructures from Water-Based Dispersions of Nanoparticles for Eco-Friendly Polymer Solar Cell Applications

“…The Forster radius for heterogeneous transfer from P3HT to PC 61 BM was previously determined to be 2.7 nm. 42 At the beginning of each simulation, energies were assigned to each site randomly from a Gaussian distribution with standard deviation 0.06 eV for P3HT and 0.09 eV for PC 61 BM. 42 The energy of each PC 61 BM site was lower than the energy of each P3HT site so that hopping from the P3HT to the PC 61 BM was always favorable.…”

“…64 We have previously shown that if the electron and hole transfer efficiencies across the donor:acceptor interface is similar, the same η ED is obtained regardless of whether heterogeneous energy transfer is taken into account. 42 Given that for the P3HT:PC 61 BM system both electron and hole transfer is near 100%, 42 heterogeneous energy transfer can be ignored when calculating the experimental η ED . The average η ED ± standard deviation for replicate measurements of each film is provided and also in table format in Table 2 UV−vis measurements were taken using an ultraviolet−visible absorption spectrophotometer (UV−vis, Varian Cary 6000i) in the wavelength range 300−800 nm.…”

A Machine Learning–Based Design Rule for Improved Open‐Circuit Voltage in Ternary Organic Solar Cells

“…In the cascade structure‐based OSCs, the HOMO and LUMO levels of the third component (known as the cascade) are located between the HOMOs and LUMOs of the donor and acceptor materials . The energy levels of the donors, acceptors, and third components must be carefully selected to form an “energy cascade structure” that can stabilize the transfer of electrons and holes between the three materials, thus increasing exciton dissociation and reducing charge recombination at each interface . Thus, designing the cascade structure‐based OSCs typically requires appropriate energy levels of third components to fabricate cascade energy heterojunction devices.…”

Fused 1,5-Naphthyridines: Synthetic Tools and Applications

“…Recently, PTNT-conjugated polymer was used as the donor polymer. The preparation of environmentally friendlier polymer solar cell devices [ 76 , 77 ].…”