Polymer/PCBM systems

Many new electron acceptor materials have been tested in the polymer BHJ blend system, including polymer polymer blend, polymerrCd, polymer oxide, i etc. However, currently they are not as effective as the polymer PCBM system. To further improve the performance of the promising polymer PF-co-DTB, we work on new fullerene derivative as electron acceptor materials. It is shown up to a large amount of (80wt.%) PCBM is required for optimal performance arising from a strong enhancement of... 

Research in the field of OPV based on small molecules or polymer/PCBM systems has developed tremendously within the past decade. Champion laboratory cells reaching efficiencies of 10% have been reported recently [132]. However, average solar cell efficiencies of optimized laboratory cells ranging in between 5 and 6% and PCE values of solar cell modules already commercially available on the market are usually lowered by a factor of about 2. 

PCBM, which represent the most often studied polymer-fullerene systems, are shown... 

With the prospect of long-term stability [185,188] and the abiUty to print polymer solar cells [188] with power conversion efficiencies of 4-5%, EQEs of over 75%, internal quantum efficiencies approaching unity [194], and fill factors of almost 70% [18,21], the P3HT PCBM system is at the moment highly optimized. The main limitations in reaching larger power conversion effiden-... 

Significant amount of research has been dedicated to two material systems MDMO-PPV PCBM (MDMO-PPV poly(2-methoxy-5-(3, 7 -dimethyl-octyloxy)-l,4-phenylenevinylene)) and RR-P3HT PCBM, which represent the state-of-the-art polymer solar cell technology. Because there are excellent review papers on the MDMO-PPV PCBM system in the literature, in this section we will only focus on the recent improvements in RR-P3HT PCBM system, especially the approaches to optimize the active blend layer for enhancing device efficiency. 

The appearance of these aggregates does not hamper photovoltaic performance of the fullerene/P3HT blends short-circuit currents and FFs of the devices become even improved in some cases. This behavior makes a sharp contrast with the MDMO-PPV/[60]PCBM and P3HT/[60]PCBM systems described above where the formation of numerous PCBM aggregates in the films immediately kills their photovoltaic performance. It might be envisioned that solar cells comprising thiophene or furane-appended fullerene derivatives (I-III) exhibit superior thermal stability because of hampered fullerene/ polymer segregation. Unfortunately, this issue was not addressed in this study. 

For the isotropic polymer PCBMS , the values obtained at the plateau level of orientation ( 0.3) for ds3 and d3i were 12.8 and 2.13 pmA, respectively. These data give a ratio d33/d3i of 6, which exceeds the theoretical value of 3 predicted for isotropic systems (cf Table 2). 

The use of Pt-acetylides containing phosphine ligands was extended further by the Schanze group in 2006 [84, 85], In one contribution, they incorporated platinum-acetylide polymers into photovoltaic devices which demonstrate good device efficiency. Transient absorption studies provide definitive evidence for photoinduced electron transfer from the Pt-acetylide to PCBM by the temporal evolution of the TA spectrum, observing the formation of the PCBM radical anion at 1,050 nm. The same system was eventually demonstrated to operate as a bulk heterojunction photovoltaic device [84],... 

At this point it is noteworthy to compare our results on the variation of eharge earrier mobilities with composition of the blends to other ambipolar mixed systems. There are on the one hand polymer-fiillerene blends used for photovoltaie applieations (in particular MDMO-PPV PCBM) [44, 45] and on... 

We have shown nanomorphology of the composite layer strongly influences the BHJphotovoltaic performanceinRR-P3HT PCBMsystem. This is also truefor the low band-gap polymer system when C70-PCBM is used. Because C70-PCBM... 

The influence of morphology formation on the performance of PSCs was first observed for systems where PCBM was blended with the electron-donor polymer poly[2-mefhoxy-5-(3, 7 -dimethyloctyloxy)-l,4-phenylene vinylene] (MDMO-PPV). A strong increase in power conversion efficiency was obtained by changing the solvent from toluene (0.9% efficiency) to chlorobenzene (2.5% efficiency) [13]. The better performance of MDMO-PPV/PCBM PSCs in case of using chlorobenzene (or o-dichlorobenzene) as a solvent rather than toluene was found to be due to smaller and thus more favorable scale of phase segregation (Figure 2.5). The higher... 

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