Heterojunction photovoltaic cell

Peumans, P. Uchida, S. Forrest, S. R. 2003. Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films. Nature 425 158-162. 

Figure 4.28 Dye-polymer blend, distributed heterojunction photovoltaic cell.

Xue JG, Rand BP, Uchida S, Eorrest SR (2005) A hybrid planar-mixed molecular heterojunction photovoltaic cell. Adv Mater 17 66... 

Besides ruthenium complexes, rhenium complexes were also used as the photosensitizers in photovoltaic cells. Bulk heterojunction photovoltaic cells fabricated from sublimable rhenium complexes exhibited a power conversion efficiency of 1.7%.75,76 The same rhenium complex moiety was incorporated into conjugated polymer chains such as polymer 16a c (Scheme 9). Fabrication of devices based on conjugated rhenium containing polymers 17a c and SPAN by the LbL deposition method was reported.77 The efficiencies of the devices are on the order of 10 4%. 

In a bulk-heterojunction photovoltaic cell with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as an electron acceptor, alternating copolymer 19 (Fig. 9), derived from 2,7-fluorene and 2,5-dithienylsilole, can show impressive performance as the electron donor.31 In a device configuration of ITO/PEDOT/active layer/Ba/Al, the dark current density—bias curve shows a small leakage current, suggesting a continuous, pinhole-free active layer in the device. Under illumination of an AM 1.5 solar simulator at 100 mW/cm2, a high short-circuit current of 5.4 mA/cm2, an open-circuit voltage of 0.7 V, and a fill factor of 31.5% are achieved. The calculated energy conversion efficiency is 2.01%. 

For proper operation of a bulk heterojunction photovoltaic cell, a special alignment of the HOMO and LUMO levels of the bulk heterojunction components must be accomplished, compatible with the electrodes work functions, as depicted in Scheme 5.8. If an exciton is formed in the polymer phase, then the electron is transferred to the NC phase and reaches the aluminum electrode via its percolating pathway. The remaining hole is transported to the ITO electrode through the polymer phase. In the alternative case, that is, the formation of an exciton in the NCs phase, the hole is transferred to the polymer phase and then transported to the ITO electrode, whereas the electron reaches the aluminum electrode through the NCs phase. 

Figure 17. Energetic scheme of electron transfer processes taking place in a dye-sensitized heterojunction photovoltaic cell. Also shown is the structure of the spiro-MeOTAD molecule that constitutes an efficient organic hole transport material (HTM).

Halls JJM, Pichler K, Friend RH, Moratti SC, Holmes AB (1996) Exdton diffusion and dissociation in a poly(p-phenylenevinylene)/C6o heterojunction photovoltaic cell. Appl Phys Lett 68 3120... 

Wienk MM, Kroon JM, Verhees WJH, Knol J, Hummelen JC, van Hall PA, Janssen RAJ (2003) Efficient methano[70]fullerene/MDMO-PPV bulk heterojunction photovoltaic cells. Angew Chem Int Ed 42 3371... 

Finally, conjugated materials 40 based on poly(phenylene thiophene) and poly (fluorene thiophene) main chain polymers functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. Heterojunction photovoltaic cells with the simple structure ITO/polymer/C-60/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53-2.58 mAcm 2, 0.12-0.24 V, and 0.084-0.12%, respectively [77]. 

Yang, R, Shtein, M., and Forrest, S.R., Controlled growth of a molecular bulk heterojunction photovoltaic cell, Nat. Mater. 4, 37 1, 2005. 

Device Performance of CuPcrQo Mixed Heterojunction Photovoltaic Cells... 

J. Seo, M. J. Cho, D. Lee, A. N. Cartwright, P. N. Prasad, Efficient Heterojunction Photovoltaic Cell Utilizing Nanocomposites of Lead Sulfide Nanocrystals and a Low-Bandgap Polymer. Advanced Materials 2011, 23, 3984-3988. 

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