Saranin Danila S, Mahmoodpoor Abolfazl, Voroshilov Pavel M, Simovski Constantin R, Zakhidov Anvar A
National University of Science and Technology MISiS, Moscow 119049, Russia.
ITMO University, Kronverkskiy pr. 49, St. Petersburg 197101, Russia.
ACS Appl Mater Interfaces. 2021 Feb 24;13(7):8606-8619. doi: 10.1021/acsami.0c17865. Epub 2021 Feb 15.
We demonstrate an improvement in the performance of organic photovoltaic (OPV) systems based on small molecules by ionic gating via controlled reversible n-doping of multi-wall carbon nanotubes (MWCNTs) coated on fullerene electron transport layers (ETLs): C and C. Such electric double-layer charging (EDLC) doping, achieved by ionic liquid (IL) charging, allows tuning of the electronic concentration in MWCNTs and the fullerene planar acceptor layers, increasing it by orders of magnitude. This leads to the decrease of the series and increase of the shunt resistances of OPVs and allows use of thick (up to 200 nm) ETLs, increasing the durability of OPVs. Two stages of OPV enhancement are described upon the increase of gating bias : at small (or even zero) , the extended interface of ILs and porous transparent MWCNTs is charged by gating, and the fullerene charge collector is significantly improved, becoming an ohmic contact. This changes the S-shaped - curve via improving the electron collection by an n-doped MWCNT cathode with an ohmic interfacial contact. The - curves further improve at higher gating bias due to the increase of the Fermi level and decrease of the MWCNT work function. At the next qualitative stage, the acceptor fullerene layer becomes n-doped by electron injection from MWCNTs while ions of ILs penetrate into the fullerene. At this step, the internal built-in field is created within OPV, which helps in exciton dissociation and charge separation/transport, increasing further the and the fill factor. The ionic gating concept demonstrated here for most simple classical planar small-molecule OPV cells can be potentially applied to more complex highly efficient hybrid devices, such as perovskite photovoltaic with an ETL or a hole transport layer, providing a new way to tune their properties via controllable and reversible interfacial doping of charge collectors and transport layers.
我们展示了基于小分子的有机光伏（OPV）系统性能的提升，该提升通过对涂覆在富勒烯电子传输层（ETL）：C和C上的多壁碳纳米管（MWCNT）进行可控的可逆n型掺杂实现离子门控。这种通过离子液体（IL）充电实现的双电层充电（EDLC）掺杂，能够调节MWCNT和富勒烯平面受体层中的电子浓度，使其增加几个数量级。这导致OPV的串联电阻降低，并联电阻增加，并允许使用厚达200nm的ETL，从而提高OPV的耐久性。随着门控偏压的增加，描述了OPV增强的两个阶段：在小（甚至零）偏压下，IL与多孔透明MWCNT的扩展界面通过门控充电，富勒烯电荷收集器得到显著改善，成为欧姆接触。这通过改善具有欧姆界面接触的n型掺杂MWCNT阴极的电子收集来改变S形J - V曲线。由于费米能级的增加和MWCNT功函数的降低，J - V曲线在更高的门控偏压下进一步改善。在下一个定性阶段，受体富勒烯层通过从MWCNT注入电子而成为n型掺杂，同时IL的离子渗透到富勒烯中。在这一步，OPV内部产生内置电场，这有助于激子解离和电荷分离/传输，进一步提高Jsc和填充因子。这里展示的离子门控概念，对于最简单的经典平面小分子OPV电池而言，有可能应用于更复杂的高效混合器件，如带有ETL或空穴传输层的钙钛矿光伏电池，为通过电荷收集器和传输层的可控且可逆的界面掺杂来调节其性能提供了一种新方法。
