|New research shows that the future of lighter, cheaper and more-flexible solar cells looks bright. Scientists at Ohio State University added silver nanoparticles to their polymer semiconductor photovoltaic materials and observed a relative efficiency boost of 12%. The discovery could pave the way to flexible organic photovoltaics with all the advantages of ease of manufacture and inexpensive starting materials.
To prepare their modified organic photovoltaic materials, the team created a colloidal solution of silver nanoparticles. Organic capping groups stabilize the nanoparticles and prevent them from sticking together. Transmission electron microscopy reveals that the particles are highly uniform in size, with an average diameter of about 4 nanometres, and align into a regular mosaic with controlled spacing between them, which could be key to light absorption. The team then applied this colloidal preparation to their organic bulk heterojunction photovoltaic devices, which are constructed from a polythiophene-fullerene material on an indium-tin oxide/glass substrate. The team reported to have got 70 amps/sq mtr with the silver nanoparticles, only 62 amps without the additive.
Their initial tests revealed that the nanolayer boosts optical absorption and photocurrent for the photovoltaic devices because an increased electric field is induced in the photoactive layer by the excited localized surface plasmons of the silver nanoparticles. In other words, the nanotechnology essentially amplifies the signal by absorbing solar energy from a wider range of wavelengths. The light absorption of polymer solar cells is inadequate as currently, top-performing materials have an overall efficiency of about 5%. Even with the relatively low production cost of polymers compared to other solar cell materials, efficiency needs to be boosted to at least 10% to turn a profit. The new research is expected to yield more efficiency as by changing the organic coating, the spacing of the particles can be changed and size of each particle can be altered. By fine-tuning the mosaic pattern, the team could move the enhanced absorption to different wavelengths, for increased improvement.
A team of Australian and US researchers has developed a multi-cell array that achieved an efficiency of 43%, beating the previous world record by 0.3%, setting a new record for solar cell efficiency. Solar cells only convert a fraction of the energy from sunlight into electricity. To create electricity, each photon of light must have enough energy to free an electron inside the solar cell. If the energy is low, the photon will bounce off the solar cell, and no electrical current will be created. A standard cell can respond to photons of certain energy and above, but not below. Silicon, which is used in most solar cells, has a low threshold ensuring most wavelengths of visible light will free an electron. But, they are inefficient converters of short wavelengths such as blue light. To achieve a higher rate of conversion, the researchers used 5 different solar cell types matched to different wavelengths of light, wherein each cell has the maximum efficiency for one particular colour. Using filters, the solar cell splits the incoming light into its different wavelength bands and sends it to the different cells. The UNSW researchers developed a cell that efficiently converts red light into electricity. The team�s cell works efficiency over the red end of the solar spectrum. The team combined it with cells that had done well over other wavelength ranges, so as to improve efficiency. The other four cells were developed by two US groups based at the National Renewable Energy Laboratory and Emcore Corporation. Instead of silicon, these cells used combinations of gallium, indium, phosphorus and arsenic.