A novel device architecture for high-performance organic solar cells

英国的发电量为408太瓦时/年(相当于平均46.6千兆瓦)，占英国二氧化碳排放量的32%。这由煤炭(37%)、天然气(36%)、核能(18%)、水电(0.9%)和其他可再生能源(3.2%)提供。为了减少英国的排放，我们必须增加低排放技术在我们发电中的比例。太阳能特别有吸引力，因为可用能源的数量比任何其他可再生能源都大，主要是因为最终太阳能为这些能源提供了所有能源。光伏发电将需要成为家庭发电的重要组成部分，特别是如果制定新的立法要求新家庭实现碳中性的话。到目前为止，每瓦峰值成本为3-5美元的传统硅太阳能电池与传统电源相比，在成本上还不具竞争力。由于溶液可加工有机半导体与基于印刷的制造和低成本柔性衬底的兼容性，激子有机太阳能电池正在成为一种有趣的可再生能源发电技术。近年来，在器件性能方面取得了很大进展，但有机太阳能电池的性能仍不能满足实际应用的要求。有机太阳能电池已经在许多不同的材料体系中得到了验证。目前，性能最好的能量转换效率为5%的体系是半导体聚噻吩基聚合物与富勒烯的可溶性衍生物的混合物。此外，两种聚合物的混合显示出约3%的效率。这些效率仍然远低于理论上的限制和应用要求。电力成本是由制造光伏组件/系统的成本、组件的效率和使用寿命共同决定的。通常认为，为了能够在例如建筑集成光伏中实现实际应用，需要10%的最小功率转换效率。为了实现这一雄心勃勃的效率目标，需要新的方法来最大限度地减少电池中的所有能源损失。一种重要的损耗机制是由于电池中不同材料之间的界面处的能量损耗。在有机太阳能电池中，电子和空穴对是由光吸收产生的，但由于这些材料中非常强的、未屏蔽的库仑相互作用，电子和空穴形成了强束缚激子。为了产生光电流，激子需要分裂，而激子只能在两种不同材料之间的界面上发生，一种接受电子，另一种接受空穴。界面电荷分离的驱动力构成了显著的能量损失机制，并特别限制了电池的开路电压。在本项目中，我们提出了一种新的有机光电二极管的器件结构，它应该允许利用沿聚合物主干的快速载流子传输来最小化界面能量损失，同时保持较低的复合损失。该项目是一项可行性研究，将确定是否可以通过沿着器件中存在的电场方向对齐聚合物链来显着减少复合损失。我们从对其他器件结构的测量中获得了间接证据，表明这是可能的，目前的可行性研究将确定是否可以利用这种效应来提高最先进的有机太阳能电池系统的效率，以达到10%的电力转换效率。

The UK generates electricity at a rate of 408 TWh/a (equivalent to an average of 46.6 GW) and this accounts for 32% of the UK's CO2 emissions. This is supplied by coal (37%), gas (36%), nuclear (18%), hydro (0.9%) and other renewables (3.2%). To reduce the UK's emissions, we must increase the fraction of our electricity generated by low emission technologies. Solar energy is particularly attractive because the amount of energy available is larger than for any other renewable source, principally because ultimately the sun provides all the energy for these sources. Photovoltaics will need to become an important part of generating household electricity, particularly if new legislation is put in place requiring new homes to be carbon neutral. To date conventional silicon solar cells that cost $3-5 per Watt peak are not cost competitive with conventional sources of electricity. Excitonic organic solar cells are becoming an interesting technology for renewable energy generation due to the compatibility of solution-processible organic semiconductors with printing-based manufacturing and low-cost flexible substrates. Much progress has been made in recent years in terms of device performance, but the performance of organic solar cells is still not meeting requirements for practical applications. Organic solar cells have been demonstrated with a number of different materials systems. At present the best performing system with energy conversion efficiencies of 5% are mixtures of a semiconducting polythiophene based polymer with a soluble derivative of fullerence. Also blends of two polymers have shown efficiencies on the order of 3%. These efficiencies are still well below theoretical limits and requirements for applications. The cost of electricity is determined by a combination of the cost of manufacturing the photovoltaic module / system, the efficiency of the module and its lifetime. It is generally considered that a minimum power conversion efficiency of 10% is needed in order to enable realistic applications in, for example, in building integrated photovoltaics. To achieve this ambitious efficiency target novel approaches are needed to minimize all sources of energy loss in the cell. One significant loss mechanism is due to energetic losses at the interfaces between the different materials in the cell. In an organic solar cell electron and hole pairs are generated by absorption of light, but due to the very strong, unscreened Coulomb interaction in these materials, the electron and hole form a strongly bound exciton. To generate a photocurrent the exciton needs to be split up, and these can only occur at an interface between two different materials, one accepting the electron, and the other one taking the hole. The driving force for charge separation at the interface constitues a signifcant energy loss mechanism, and limits in particular the open circuit voltage of the cell. In the present project we propose a new device architecture for an organic photodiode that should allow exploiting the fast carrier transport along the polymer backbone to minimize the interfacial energy losses while keeping recombination losses low. The project is a feasibility study which will establish whether by aligning the polymer chains along the direction of the electric field that is present in the device it is possible to reduce recombination losses significantly. We have got indirect evidence from measurements on other device structures that this is possible, and the present feasibility study will establish whether this effect can be exploited for improving the efficiency of state-of-the-art organic solar cell systems towards reaching power conversion efficiencies of 10%.