Polymer power conversion efficiency

Comparison of the spectral response and of the power efficiency of these first conjugated polymer/fullerene bilayer devices with single layer pure conjugated polymer devices showed that the large potential of the photoinduced charge transfer of a donor-acceptor system was not fully exploited in the bilayers. The devices still suffer from antibatic behavior as well as from a low power conversion efficiency. However, the diode behavior, i.e. the rectification of these devices, was excellent. 

Liang YY, Xu Z, Xia JB, Tsai ST, Wu Y, Li G, Ray C, Yu LP (2010) For the bright future-bulk heterojunction polymer solar cells with power conversion efficiency of 7.4%. Adv Mater 22 E135... 

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%. 

Photovoltaic cells with the simple device structure ITO/polymer/C6o/Al were fabricated. The power conversion efficiencies of the devices fabricated... 

The photovoltaic properties of other Pt-acetylide polymers 31 were published by the same group (Scheme 16). The aromatic linking units were modified, and the power conversion efficiency of the devices were in the range between 0.21% and 2.66%.94 A review article dedicated to the optical properties of this group of Pt acetylide polymers has been published.95... 

Physical incorporatiem of phthalocyanines and porphyrins in polymers was mentioned in Chap. 2.1.1 and 2.1.2. Moreover, photovoltaic properties of Schottky bavier solar cells were checked by dispersing metal free Pc in a polymer binder At peak solar power (135 mW/cm ) a power conversion efficiency of 1,2% has been obtained. 

Figure 2. Photocurrent-voltage curves (10 mV/s) for a p-type Si/[(PQ 2C )J Pd(0)]mrt photocathode where Pd(0) is deposited only on the outer surface of the redox polymer. The illumination source is a He-Ne laser, 632.8 nm, at 10 mW/ cm2, and the exposed electrode area is 0.1 cmi2. The inset shows the power conversion efficiency peaking at pH = 4. Steady-state photocurrent corresponds to H, evolution. Data are from Ref. 35.

To help the design of optimized polymeric materials for BHJ solar cells, several models have been recently proposed [87-89]. The combination of these models and DFT calculations has recently led to the synthesis of several other poly(2,7-carbazole) derivatives (P17, P19-P22). Symmetric polymers (P17-P19) show better structural organization than asymmetric polymers (P20-P22), resulting in higher hole mobilities and power conversion efficiencies. Moreover, their low HOMO energy levels (ca. (- 5.6)—(— 5.4)eV) provide an excellent air stability and relatively high Voc values (between 0.71-0.96 V). 

Various alternative acceptor components for organic BHJ solar cells have been tried in an attempt to improve cell performance. Fullerene derivatives such as C70 PCBM and Cg4 PCBM have been used in place of Ceo PCBM, because the lower molecular symmetry compared with Ceo PCBM enables stronger light absorption by the fullerene. The C70 PCBM derivatives were relatively successful, leading to 3% power conversion efficiency for devices made with MDMO-PPV polymer (Wienk et al, 2003). The Cg4 derivatives resulted in rather poor device efficiencies, attributed to the unfavourable film morphology resulting from the immiscibility of Cs4 derivatives with typical organic solvents (Kooistra et al, 2006). 

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