Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, UK.
Nanotechnology. 2011 Jun 3;22(22):225403. doi: 10.1088/0957-4484/22/22/225403. Epub 2011 Apr 1.
Organic semiconductors employed in solar cells are perfectly stable to solar irradiation provided oxygen content can be kept below 1 ppm. Paradoxically, the state-of-the-art molecular hole-transporter-based solid-state dye-sensitized solar cells only operate efficiently if measured in an atmosphere containing oxygen. Without oxygen, these devices rapidly lose photovoltage and photocurrent and are rendered useless. Clearly this peculiar requirement has detrimental implications to the long term stability of these devices. Through characterizing the solar cells in air and in oxygen-free atmospheres, and considering the device architecture, we identify that direct contact between the metallic cathode and the mesoporous metal oxide photo-anode is responsible for a shunting path through the device. This metal-metal oxide contact forms a Schottky barrier under ambient conditions and the barrier is suitably high so as to prevent significant shunting of the solar cells. However, under light absorption in an anaerobic atmosphere the barrier reduces significantly, opening a low resistance shunting path which dominates the current-voltage characteristics in the solar cell. By incorporating an extra interlayer of insulating mesoporous aluminum oxide, on top of the mesoporous semiconducting metal oxide electrode, we successfully block this shunting path and subsequently the devices operate efficiently in an oxygen-free atmosphere, enabling the possibility of long term stability of solid-state dye-sensitized solar cells.
在太阳能电池中使用的有机半导体，如果能将氧含量保持在 1ppm 以下，则对太阳辐射是完全稳定的。矛盾的是，最先进的基于分子空穴传输体的固态染料敏化太阳能电池只有在含氧的环境中测量才能高效运行。没有氧气，这些设备会迅速失去光电压和光电流，变得毫无用处。显然，这种特殊的要求对这些设备的长期稳定性有不利影响。通过在空气和无氧环境中对太阳能电池进行特性分析，并考虑器件结构，我们发现金属阴极和介孔金属氧化物光阳极之间的直接接触是导致器件分流的原因。在环境条件下，这种金属-金属氧化物接触形成肖特基势垒，势垒足够高，从而防止太阳能电池的明显分流。然而，在无氧环境下吸收光时，势垒会显著降低，形成低电阻分流路径，从而主导太阳能电池的电流-电压特性。通过在介孔半导体金属氧化物电极的顶部增加一层绝缘介孔氧化铝的额外中间层，我们成功地阻断了这种分流路径，随后，设备在无氧环境下高效运行，从而使固态染料敏化太阳能电池具有长期稳定性的可能性。
