Title: Mixed-quantum-dot solar cells
Abstract: Colloidal quantum dots are emerging solution-processed materials for large-scale and low-cost photovoltaics. The recent advent of quantum dot inks has overcome the prior need for solid-state exchanges that previously added cost, complexity, and morphological disruption to the quantum dot solid. Unfortunately, these inks remain limited by the photocarrier diffusion length. Here we devise a strategy based on n- and p-type ligands that judiciously shifts the quantum dot band alignment. It leads to ink-based materials that retain the independent surface functionalization of quantum dots, and it creates distinguishable donor and acceptor domains for bulk heterojunctions. Interdot carrier transfer and exciton dissociation studies confirm efficient charge separation at the nanoscale interfaces between the two classes of quantum dots. We fabricate the first mixed-quantum-dot solar cells and achieve a power conversion of 10.4%, which surpasses the performance of previously reported bulk heterojunction quantum dot devices fully two-fold, indicating the potential of the mixed-quantum-dot approach.
中文摘要：
膠體量子點材料十分適合製作大面積、低成本的太陽能電池。過去關於量子點電池的製備研究多採取固相配體交換法，其製作工藝成熟並且器件性能穩定。但是由於利用多步法製作方式，製作過程需要耗費相當多的原材料。最近關於「量子點墨水」電池的研究進展在對器件效率進行進一步提升的同時有效地減少原材料損耗，但是其效率依然受制於光生載流子的低擴散長度。在這項工作中，Zhenyu Yang，Jame Fan和Andrew Proppe等人利用表面化學方法合成了p型和n型兩種量子點墨水。他們通過合理調節其配比製成混合量子點墨水，在常溫下的混合墨水的旋塗以及後續處理成功製備具有體異質結的量子點太陽能電池。一系列的表面化學表徵方法證明在混合後兩種量子點的表面配體和自身禁帶特性不會受到處理方式的影響。此外，作者通過載流子在量子點間的遷移以及激子分離等超快光譜的研究證實了量子點混合薄膜中的電荷分離效率較單一種類的量子點固體有所提高。作者進一步運用這種混合墨水製作了太陽能電池，其最高光電轉換效率高於單一n型墨水電池組件的效率，達到了10.4%，並刷新了量子點體異質結電池效率的記錄。