Offset energies at organic semiconductor heterojunctions and their influence on the open-circuit voltage of thin-film solar cells
Offset energies at organic semiconductor heterojunctions and their influence on the open-circuit voltage of thin-film solar cells
复制标题
DOI：
10.1103/physrevb.75.115327
复制
发表时间：
2007-03-01
影响因子：
3.7
通讯作者：
Forrest, Stephen R.
中科院分区：
文献类型：
--
作者：
Rand, Barry P.;Burk, Diana P.;Forrest, Stephen R.
有机半导体异质结（HJ）的能级偏移采用Marcus电子转移理论和广义Shockley暗电流密度-电压（J-V）特性理论相结合的方法来模拟。该模型用于拟合薄膜有机光伏电池中常用的几种给体-受体组合的J-V特性。结合施主-受主结的能量学测量，该模型预测结开路电压（V-OC）和短路电流密度（J（SC））之间的权衡。发现14个供体-受体HJ材料对的V-OC随光强度增加而增加，与温度成反比。特别是，我们发现，V-OC达到最大值在低温（类似于175 K）的异质结研究的许多。V-OC的最大值是供体电离势和受体电子亲合势之间的差减去解离的成对电子-空穴对的结合能的函数：这是对有机异质结的电荷转移机制具有影响的一般关系。由该模型提供的基本理解使我们推断双异质结构有机光伏电池的最大功率转换效率可以高达12%。当与混合层结合以增加光电流和堆叠电池以增加V-OC时，接近16%的效率是可以达到的。
Organic semiconductor heterojunction (HJ) energy level offsets are modeled using a combination of Marcus theory for electron transfer, and generalized Shockley theory of the dark current density vs voltage (J-V) characteristics. This model is used to fit the J-V characteristics of several donor-acceptor combinations commonly used in thin film organic photovoltaic cells. In combination with measurements of the energetics of donor-acceptor junctions, the model predicts tradeoffs between the junction open-circuit voltage (V-OC) and short-circuit current density (J(SC)). The V-OC is found to increase with light intensity and inversely with temperature for 14 donor-acceptor HJ materials pairs. In particular, we find that V-OC reaches a maximum at low temperature (similar to 175 K) for many of the heterojunctions studied. The maximum value of V-OC is a function of the difference between the donor ionization potential and acceptor electron affinity, minus the binding energy of the dissociated, geminate electron-hole pair: a general relationship that has implications on the charge transfer mechanism at organic heterojunctions. The fundamental understanding provided by this model leads us to infer that the maximum power conversion efficiency of double heterostructure organic photovoltaic cells can be as high as 12%. When combined with mixed layers to increase photocurrent and stacked cells to increase V-OC, efficiencies approaching 16% are within reach.