卤化铅可用作新式太阳能电池的原材料

Photovoltaic（光电的） energy conversion¹ offers one of the best means for the future of renewable energy in the world. The efficiency of solar cells depends heavily upon the light-absorbing materials they use. Photovoltaic systems based on lead halide perovskite are a new, revolutionary type of device with efficiencies currently exceeding 16%. However, a detailed² description of how these solar cells turn light into electrical current is still lacking. Publishing in Nature Photonics, scientists from EPFL have investigated how the generated electrical charge travels across the perovskite（钙钛矿） surface of solar cells built with different architectures. Lead halide perovskites are materials that have recently attracted an immense interest, as solar cells based on these semiconductors⁴ demonstrate very high conversion efficiencies and an unsurpassed cell voltage of more than 1 V. However, it is not entirely⁵ clear how they work. A better understanding of their functioning mechanisms⁶ would help improve them in the future or even open up novel technologies with increased efficiency.

 

The groups of Michael Grätzel and Jaques E. Moser at EPFL, working with the Institute for Solar Fuels in Berlin, have used time-resolved spectroscopy techniques to determine how charges move across perovskite surfaces. The researchers worked on various cell architectures, using either semiconducting titanium dioxide or insulating aluminum⁸ trioxide films. Both porous⁹（多孔的） films were impregnated with lead iodide perovskite (CH3NH3PbI3) and an organic "hole-transporting material," which helps extracting positive charges following light absorption. The time-resolved techniques included ultrafast laser spectroscopy and microwave photoconductivity.

 

The results showed two main dynamics¹⁰. First, that charge separation, the flow of electrical charges after sunlight reaches the perovskite light-absorber, takes place through electron transfer at both junctions¹¹ with titanium dioxide and the hole-transporting material on a sub-picosecond timescale. Secondly¹², the researchers found that charge recombination was significantly slower for titanium oxide⁷ films rather than aluminum ones. Charge recombination is a detrimental¹³ process wasting the converted energy into heat and thus reducing the overall efficiency of the solar cell.

 

The authors state that lead halide perovskites constitute unique semiconductor³ materials in solar cells, allowing ultrafast transfer of electrons and positive charges at two junctions simultaneously¹⁴ and transporting both types of charge carriers quite efficiently¹⁵. In addition, their findings show a clear advantage of the architecture based on titanium dioxide films and hole-transporting materials.

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