Lin Hsi-Kuei, Li Jia-Xing, Wang Hao-Cheng, Su Yu-Wei, Wu Kaung-Hsiung, Wei Kung-Hwa
Department of Materials Science and Engineering, National Chiao Tung University 300 Hsinchu Taiwan
Department of Electrophysics, National Chiao Tung University 300 Hsinchu Taiwan.
RSC Adv. 2018 Apr 4;8(23):12526-12534. doi: 10.1039/c8ra01532e. eCollection 2018 Apr 3.
In photovoltaic devices, more effective transfer of dissociated electrons and holes from the active layer to the respective electrodes will result in higher fill factors and short-circuit current densities and, thus, enhanced power conversion efficiencies (PCEs). Planar perovskite photovoltaics feature an active layer that can provide a large exciton diffusion length, reaching several micrometers, but require efficient carrier transport layers for charge extraction. In this study, we employed two nanocomposite carrier transfer layers-an electron transport layer (ETL) comprising [6,6]phenyl-C-butyric acid methyl ester (PCBM) doped with the small molecule 4,7-diphenyl-1,10-phenanthroline (Bphen), to enhance the electron mobility, and a hole transfer layer (HTL) comprising poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) doped with molybdenum disulfide (MoS) nanosheets, to enhance the hole mobility. We used ultraviolet photoelectron spectroscopy to determine the energy levels of these composite ETLs and HTLs; atomic force microscopy and scanning electron microscopy to probe their surface structures; and transmission electron microscopy and synchrotron grazing-incidence small-angle X-ray scattering to decipher the structures of the ETLs. Adding a small amount (less than 1%) of Bphen allowed us to tune the energy levels of the ETL and decrease the size of the PCBM clusters and, therefore, generate more PCBM aggregation domains to provide more pathways for electron transport, leading to enhanced PCEs of the resulting perovskite devices. We used quantitative pump-probe data to resolve the carrier dynamics from the perovskite to the ETL and HTL, and observed a smaller possibility of carrier recombination and a shorter injection lifetime in the perovskite solar cell doubly modified with carrier transport layers, resulting in an enhancement of the PCE. The PCE reached 16% for a planar inverted perovskite device featuring an ETL incorporating 0.5 wt% Bphen within PCBM and 0.1 wt% MoS within PEDOT:PSS; this PCE is more than 50% higher than the value of 10.2% for the corresponding control device.
在光伏器件中，将离解的电子和空穴从活性层更有效地传输到各自的电极，将导致更高的填充因子和短路电流密度，从而提高功率转换效率（PCE）。平面钙钛矿光伏器件的活性层能够提供较大的激子扩散长度，可达几微米，但需要高效的载流子传输层来进行电荷提取。在本研究中，我们采用了两种纳米复合载流子传输层——一种电子传输层（ETL），由掺杂有小分子4,7-二苯基-1,10-菲咯啉（Bphen）的[6,6]苯基-C-丁酸甲酯（PCBM）组成，以提高电子迁移率；另一种空穴传输层（HTL），由掺杂有二硫化钼（MoS）纳米片的聚（3,4-乙撑二氧噻吩）：聚苯乙烯磺酸盐（PEDOT:PSS）组成，以提高空穴迁移率。我们使用紫外光电子能谱来确定这些复合ETL和HTL的能级；使用原子力显微镜和扫描电子显微镜来探测它们的表面结构；使用透射电子显微镜和同步加速器掠入射小角X射线散射来解析ETL的结构。添加少量（小于1%）的Bphen使我们能够调节ETL的能级并减小PCBM团簇的尺寸，因此产生更多的PCBM聚集域，为电子传输提供更多途径，从而提高所得钙钛矿器件的PCE。我们使用定量泵浦-探测数据来解析从钙钛矿到ETL和HTL的载流子动力学，并观察到在载流子传输层双重修饰的钙钛矿太阳能电池中，载流子复合的可能性较小且注入寿命较短，从而提高了PCE。对于一种平面倒置钙钛矿器件，其ETL在PCBM中掺入0.5 wt%的Bphen且HTL在PEDOT:PSS中掺入0.1 wt%的MoS，PCE达到了16%；该PCE比相应的对照器件的10.2%的值高出50%以上。
