A novel device architecture for high-performance organic solar cells

英国的发电量为408 TWh/a（相当于平均46.6 GW），占英国二氧化碳排放量的32%。这是由煤炭（37%），天然气（36%），核能（18%），水力（0.9%）和其他可再生能源（3.2%）提供的。为了减少英国的排放，我们必须增加低排放技术产生的电力比例。太阳能特别有吸引力，因为可用的能量比任何其他可再生能源都大，主要是因为太阳最终为这些能源提供了所有能量。光化学将需要成为家庭发电的重要组成部分，特别是如果新的立法要求新的房屋是碳中和的话。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没有成本竞争力。激子有机太阳能电池由于溶液可加工的有机半导体与基于印刷的制造和低成本柔性基板的兼容性而成为用于可再生能源发电的有趣技术。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然不能满足实际应用的要求。有机太阳能电池已经用许多不同的材料系统进行了展示。目前，具有5%的能量转换效率的最佳性能系统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。两种聚合物的共混物也显示出约3%的效率。这些效率仍远低于理论限制和应用要求。电力成本由制造光伏模块/系统的成本、模块的效率及其寿命的组合决定。通常认为，需要10%的最小功率转换效率，以便实现例如在建筑集成光电子中的实际应用。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量损失。一个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，电子和空穴对通过光的吸收产生，但由于这些材料中非常强的未屏蔽库仑相互作用，电子和空穴形成强束缚激子。为了产生光电流，激子需要分裂，而这些只能发生在两种不同材料之间的界面上，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一个重要的能量损失机制，特别是限制了电池的开路电压。在本项目中，我们提出了一种新的器件架构的有机光电二极管，应允许利用快速载流子传输沿着聚合物主链，以尽量减少界面能量损失，同时保持复合损失低。该项目是一项可行性研究，将确定是否通过沿器件中存在的电场方向沿着排列聚合物链，可以显著降低复合损耗。我们已经从其他器件结构的测量中获得了间接证据，证明这是可能的，目前的可行性研究将确定这种效应是否可以用于提高最先进的有机太阳能电池系统的效率，以达到10%的功率转换效率。

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%.