Search

We report the first results on conformal deposition of parylene on plastic solar cells, and study the effects of protection on performance characteristics of polymer solar cell. We show that single parylene coating layer is not a very effective barrier even for thicknesses as large as 10 μm. Our results support the experimental observations that the main degradation processes in poly(3-hexylthiophene) are the oxygen-assisted photochemical reactions, such as photobleaching and chain scission. Multilayer barriers made of parylene and aluminum oxide coatings are very promising for full protection of organic solar cell from degradation even under intense AM1.5 solar light.

A detailed study of the postproduction heat treatment of organic solar cells based on regio-regular poly(3-hexylthiophene) (RR-P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) is presented. The efficiency of the devices was significantly improved by postproduction heat treatment and both the optimal annealing temperature and optimal annealing time were determined. The phase separation of PCBM and RR-P3HT into bi-continuous network structure occurs within a very short period of time and is very stable.

We present this detailed study of a postproduction heat treatment of flexible organic solar cells based on regio-regular (RR) P3HT:PCBM composite in a wide temperature range from 75°C to 150°C. The efficiency of the photovoltaic device was significantly improved by postproduction heat treatment and both optimal annealing temperature and time dependencies were determined. Optimized parameters yielded >3% efficiency for devices on glass substrates and, using these optimized parameters, an efficiency of >2% was found for devices fabricated on flexible substrates. The optimal phase separation of PCBM and RR-P3HT into bi-continuous network structure occurs within a very short period of time and are very stable. We found that optimal concentration of PCBM in a RR-P3HT matrix is rather low, only 34 w.%. We show the performance of plastic solar cells fabricated on flexible substrates (ITO coated PET) using these optimized heat treatment parameters.

We report a nearly twofold increase of short circuit current: from Isc ∼ 10 mA/cm2 to Isc = 16–20 mA/cm2 in P3HT/PCBM solar cells (SC) employing freshly prepared regio-regular poly(3-hexylthiophene) (RR-P3HT) without special purification. The power conversion efficiency is enhanced to η≥ 4% as compared to our best η=3.8% in SC with commercial polymer despite the decreased filling factor (FF= 0.42, as compared to best FF = 0.59). We used our earlier found [1] procedures with optimal post heat treatment temperatures and time for our polymer SC. We also discovered a strong correlation between the device preparation procedures and performance. The optimal phase separation of PCBM and RR-P3HT into a bi-continuous network structure occurs after quite long solution stirring times (enhanced homogenization) and surprisingly very short annealing time at optimal temperature. We also found that the optimal concentration of PCBM in a RR-P3HT matrix is rather low, only c∼35 wt%, contrary to high c∼80 wt% in PPV based SC.