High photovoltage achieved in low band gap polymer solar cells by adjusting energy levels of a polymer with the LUMOs of fullerene derivatives
作者:Fengling Zhang、Johan Bijleveld、Erik Perzon、Kristofer Tvingstedt、Sophie Barrau、Olle Inganäs、Mats R. Andersson
DOI:10.1039/b811957k
日期:——
Solar cells based on organic molecules or conjugated polymers attract great attention due to their unique advantages, such as low cost, and their use in flexible devices, but are still limited by their low power conversion efficiency (PCE). To improve the PCEs of polymer solar cells, more efforts have been made to increase short-circuit current (Jsc) or open-circuit voltage (Voc). However, the trade-off between Jsc and Voc in bulk heterojunctions solar cells makes it tricky to find a polymer with a low band gap to efficiently absorb photons in the visible and near infrared region of the solar spectrum, while maintaining a high Voc in solar cells. Therefore, it is crucial to design and synthesize polymers with energy levels aligning with the LUMO (lowest unoccupied molecular orbital) of an electron acceptor to minimize the LUMO level difference between donor and acceptor to keep enough driving force for charge generation, thereby maximizing photovoltage in solar cells. Here a novel copolymer APFO-Green 9 was synthesized. Polymer solar cells based on APFO-Green 9 blended with a derivative of fullerene demonstrate high photovoltage by fine tuning the HOMO and LUMO level of APFO-Green 9. Solar cells based on APFO-Green 9 and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) present a photoresponse extended to 900 nm with Jsc of 6.5 mA cm−2, Voc of 0.81 V and PCE of 2.3% under illumination of AM1.5 with light intensity of 100 mW cm−2. As a low band gap polymer with a Voc bigger than 0.8 V, APFO-Green 9 is a promising candidate for efficient tandem solar cells.
基于有机分子或共轭聚合物的太阳能电池因其独特的优势(如低成本)以及其在柔性设备中的应用而备受关注,但其功率转换效率(PCE)仍然较低。为了提高聚合物太阳能电池的PCE,人们一直在努力提高短路电流(Jsc)或开路电压(Voc)。然而,在体异质结太阳能电池中,Jsc和Voc之间的权衡使得人们很难找到一种具有低带隙的聚合物,以有效地吸收太阳光谱中可见光和近红外区域的光子,同时保持太阳能电池的高Voc。因此,设计和合成能量级与电子受体的LUMO(最低未占分子轨道)对齐的聚合物至关重要,以尽量减少供体和受体之间的LUMO级差,从而保持足够的驱动力来产生电荷,从而最大限度地提高太阳能电池的光伏电压。这里合成了新型共聚物APFO-Green 9。基于APFO-Green 9与富勒烯衍生物共混的聚合物太阳能电池通过微调APFO-Green 9的HOMO和LUMO水平,表现出高光伏电压。基于APFO-Green 9和[6,6]-苯基-C71-丁酸甲酯([70]PCBM)的太阳能电池在AM1.5光照强度为100 mW cm-2的条件下,其光响应扩展到900 nm,Jsc为6.5 mA cm-2,Voc为0