Determination of photo-active region in organic thin film solar cells with an organic heterojunction

Osasa, Takahiro; Matsui, Y.; Matsumura, Tadayoshi; Matsumura, Michio

doi:10.1016/j.solmat.2006.06.033

Cited by 12 publications

(13 citation statements)

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“…The solar cells made of stacked TPD and C 60 layers showed a photovoltage (V oc ) as high as 0.8 V, although they showed a rather low photocurrent density, as seen in the curve marked with "without heat treatment" in Figure 2. The V oc is considerably high compared with that of typical organic solar cells with a junction of CuPc/PV or CuPc/ C 60 , which show V oc of about 0.5 V. [2,10] Kushto et al also reported that a similar solar cell made of N,N′-di-[(1-naphthalenyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (a-NPD) and C 60 shows V oc of about 0.8 V. [11] The high V oc of their and our solar cells is attributed to the large energy difference between the highest occupied molecular orbital (HOMO) level of the donor molecules (TPD, a-NPD) and the lowest unoccupied molecular orbital (LUMO) level of C 60 . For the V oc of organic thin-film solar cells, the importance of the energy difference has been discussed.…”

Section: Resultsmentioning

confidence: 85%

“…For example, the exciton diffusion length in layers of Cu-phthalocyanine (CuPc, electron donor) and 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI, electron acceptor), which are typical materials for the devices, is only about 10 nm. [2,3] This poses a serious problem of low photocurrent densities in these devices because most of the excitons generated in organic layers cannot reach the interface to generate carriers. To solve this problem, introduction of a ''bulk-heterojunction'' structure to organic solar cells has been proposed.…”

Section: Introductionmentioning

confidence: 99%

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Organic Solar Cells by Annealing Stacked Amorphous and Microcrystalline Layers

Osasa

Yamamoto

Matsumura

2007

Adv Funct Materials

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Organic solar cells were fabricated by stacking aromatic amine and C60 layers. The energy conversion efficiency of these solar cells was low because of poor photoabsorption by these layers and short diffusion length of excitons. However, the photocurrent density was increased by about 3 times by the application of heat treatment to the stacked organic layers at 140 °C, and the maximum energy conversion efficiency reached 1.1 % under AM 1.5, 100 mW cm–2 simulated solar light. The internal quantum efficiency of the photocurrent after the annealing reached about 45 %. When the aromatic amine layer was about 100 nm thick, the organic layers after the annealing showed a wrinkled structure under an optical microscope. The annealing temperature needed for the formation of this structure was in good agreement with the temperature needed for the increase in the photocurrent. The morphological change caused by the annealing was attributed to infiltration of the amorphous aromatic amine compound into grain boundaries of the microcrystalline C60 layer, resulting in expansion of the C60 layer and the wrinkled structure of the organic layers. From observation by electron microscopy, the mixed form of these two compounds near the interface was found to be suited to solar cells because the C60 and aromatic amine phases wedge each other in a direction normal to two electrodes. However, the annealing slightly lowered photovoltage of the solar cell. This effect was attributed to a partial contact of the C60 layer with a counter electrode through the aromatic amine layer.

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Section: Resultsmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Organic Solar Cells by Annealing Stacked Amorphous and Microcrystalline Layers

Osasa

Yamamoto

Matsumura

2007

Adv Funct Materials

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“…The thickness dependence of the photocurrent response in solar cells is another technique to determine L D , but a simple exponential distribution of excitons based on optical penetration depth could be misleading because of the optical interference arising from the reflective metal counter electrode [11]. Some literature taking this influence into account has been published, but we believe it is controversial to determine L D from the thickness dependence of photocurrent response on the basis of reported L D values that can vary from a few to tens of nanometers; like for example, in the case of copper Pc (CuPc) [12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Measurement of exciton diffusion lengths of phthalocyanine derivatives based on interlayer excitation transfer

Ichikawa

2013

Thin Solid Films

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“…Exciton diffusion length can be also obtained from photovoltage spectra [9], analysis of photoenhanced current [10] as well as from photocurrent generated by exciton dissociation at electrodes [11], [12] or at donoracceptor heterojunction [13]- [18]. Models of short-circuit photocurrent (J sc ) generated in photovoltaic devices and respecting reflection and interference of light in layers forming the system are presented in several works [14]- [18].…”

mentioning

confidence: 99%

“…The value of L D for CuPc has been obviously estimated many times. We can mention here at least the following: (103)nm [2], 8nm [13], (6820)nm [15], (205)nm [17], 15.7nm [18].…”

mentioning

confidence: 99%