Enhanced Charge Separation in Ternary P3HT/PCBM/CuInS2 Nanocrystals Hybrid Solar Cells

Abstract

Geminate recombination of bound polaron pairs at the donor/acceptor interface is one of the major loss mechanisms in organic bulk heterojunction solar cells. One way to overcome Coulomb attraction between opposite charge carriers and to achieve their full dissociation is the introduction of high dielectric permittivity materials such as nanoparticles of narrow band gap semiconductors. We selected CuInS2 nanocrystals of 7.4 nm size, which present intermediate energy levels with respect to poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). Efficient charge transfer from P3HT to nanocrystals takes place as evidenced by light-induced electron spin resonance. Charge transfer between nanocrystals and PCBM only occurs after replacing bulky dodecanethiol (DDT) surface ligands with shorter 1,2-ethylhexanethiol (EHT) ligands. Solar cells containing in the active layer a ternary blend of P3HT:PCBM:CuInS2-EHT nanocrystals in 1:1:0.5 mass ratio show strongly improved short circuit current density and a higher fill factor with respect to the P3HT:PCBM reference device. Complementary measurements of the absorption properties, external quantum efficiency and charge carrier mobility indicate that enhanced charge separation in the ternary blend is at the origin of the observed behavior. The same trend is observed for blends using the glassy polymer poly(triarylamine) (PTAA).

Status and prospects for ternary organic photovoltaics

“…Complementary light harvesting is achieved using materials with different absorption ranges 36,59 . Exciton dissociation is facilitated with high dielectric constant dopants that reduce the exciton binding energy 91 . Incorporation of high-mobility components can enhance charge transport efficiency 66 .…”

On the Efficiency Limit of Conjugated Polymer:Fullerene‐Based Bulk Heterojunction Solar Cells

“…Several groups have reported the implementation of high-ε small molecule, nanoparticle additives or the introduction of polar substitutes to the organic semiconductor materials. [55][56][57] Device effi ciencies were relatively low and the effect induced by the higher dielectric constant could hardly be distinguished from changes of the energetic levels in the donor-acceptor system, morphological or other changes induced by the added high-ε units. To which extent the dielectric constant, usually defi ned for macroscopic volumes, does infl uence electronic states with dimensions in the range of 1-2 nm in organic semiconductors is still controversial.…”

Template Synthesis of CuInS2 Nanocrystals from In2S3 Nanoplates and Their Application as Counter Electrodes in Dye-Sensitized Solar Cells

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] For example, CuInS 2 NCs are regarded as promising candidates as light absorber or counter electrode (CE) in dye-sensitized solar cells (DSSCs), due to the advantage of low cost and simple fabrication process. [18][19][20][21][22][23] Because the electronic structure of these materials strongly correlate with the [Cu]/[In] ratios, there is a great need to precisely control their size, shape, surface and compositions.…”