Peumans Peter, Uchida Soichi, Forrest Stephen R
Center for Photonics and Optoelectronic Materials (POEM), Department of Electrical Engineering and the Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544, USA.
Nature. 2003 Sep 11;425(6954):158-62. doi: 10.1038/nature01949.
The power conversion efficiency of small-molecular-weight and polymer organic photovoltaic cells has increased steadily over the past decade. This progress is chiefly attributable to the introduction of the donor-acceptor heterojunction that functions as a dissociation site for the strongly bound photogenerated excitons. Further progress was realized in polymer devices through use of blends of the donor and acceptor materials: phase separation during spin-coating leads to a bulk heterojunction that removes the exciton diffusion bottleneck by creating an interpenetrating network of the donor and acceptor materials. The realization of bulk heterojunctions using mixtures of vacuum-deposited small-molecular-weight materials has, on the other hand, posed elusive: phase separation induced by elevating the substrate temperature inevitably leads to a significant roughening of the film surface and to short-circuited devices. Here, we demonstrate that the use of a metal cap to confine the organic materials during annealing prevents the formation of a rough surface morphology while allowing for the formation of an interpenetrating donor-acceptor network. This method results in a power conversion efficiency 50 per cent higher than the best values reported for comparable bilayer devices, suggesting that this strained annealing process could allow for the formation of low-cost and high-efficiency thin film organic solar cells based on vacuum-deposited small-molecular-weight organic materials.
在过去十年中，小分子和聚合物有机光伏电池的功率转换效率稳步提高。这一进展主要归功于供体-受体异质结的引入，它作为强束缚光生激子的解离位点。通过使用供体和受体材料的混合物，聚合物器件取得了进一步的进展：旋涂过程中的相分离导致形成体异质结，通过创建供体和受体材料的互穿网络消除了激子扩散瓶颈。另一方面，使用真空沉积的小分子材料混合物实现体异质结却颇具难度：提高衬底温度引起的相分离不可避免地导致薄膜表面显著粗糙化，并导致器件短路。在此，我们证明在退火过程中使用金属盖来限制有机材料，可防止形成粗糙的表面形态，同时允许形成互穿的供体-受体网络。该方法导致的功率转换效率比同类双层器件报道的最佳值高出50%，这表明这种应变退火工艺可促成基于真空沉积小分子有机材料的低成本、高效率薄膜有机太阳能电池的形成。
