Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore.
School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, 639798, Singapore.
Small. 2015 Aug 5;11(29):3606-13. doi: 10.1002/smll.201403719. Epub 2015 Mar 30.
Low-temperature solution-processed CH3 NH3 PbI3 interfaced with TiO2 has recently been demonstrated as a highly successful type-II light harvesting heterojunction with ≈20% efficiency. Therefore, an efficient ultrafast photoexcited electron transfer from CH3 NH3 PbI3 to TiO2 is expected. However, by probing the photoexcited charge carrier dynamics in CH3 NH3 PbI3 /quartz, CH3 NH3 PbI3 /TiO2 (compact), and CH3 NH3 PbI3 /PCBM in a comparative study, an electron transfer potential barrier between CH3 NH3 PbI3 and the compact TiO2 (prepared with the spray pyrolysis method) formed by surface states is uncovered. Consequently, the CH3 NH3 PbI3 photoluminescence intensity and lifetime is enhanced when interfaced to compact TiO2 . The electron accumulation within CH3 NH3 PbI3 needed to overcome this interfacial potential barrier results in the undesirable large current-voltage hysteresis observed for CH3 NH3 PbI3 /TiO2 planar heterojunctions. The findings in this study indicate that careful surface engineering to reduce this potential barrier is key to pushing perovskite solar cell efficiencies toward the theoretical limit.
低温溶液处理的 CH3 NH3 PbI3 与 TiO2 界面最近被证明是一种高效的 II 型光收集异质结，其效率约为 20%。因此，预计 CH3 NH3 PbI3 到 TiO2 的超快光激发电子转移将非常有效。然而，通过在 CH3 NH3 PbI3 /石英、CH3 NH3 PbI3 /TiO2（致密）和 CH3 NH3 PbI3 /PCBM 中进行对比研究，探测 CH3 NH3 PbI3 中的光激发载流子动力学，在 CH3 NH3 PbI3 和由表面态形成的致密 TiO2（用喷雾热解法制备）之间发现了电子转移势垒。因此，当与致密 TiO2 接触时，CH3 NH3 PbI3 的光致发光强度和寿命增强。为了克服这个界面势垒，CH3 NH3 PbI3 内的电子积累导致观察到 CH3 NH3 PbI3 /TiO2 平面异质结中不理想的大电流-电压滞后。本研究的结果表明，进行仔细的表面工程以降低这个势垒是推动钙钛矿太阳能电池效率向理论极限迈进的关键。
