左旋多巴和N,N-二甲基亚砜共掺杂PEDOT:PSS作为空穴传输层的高性能p-i-n型钙钛矿太阳能电池

L-3,4-dihydroxyphenylalanine and Dimethyl Sulfoxide Codoped PEDOT:PSS as a Hole Transfer Layer: towards High-Performance Planar p-i-n Perovskite Solar Cells

在p-i-n型的钙钛矿太阳能电池中,聚3,4-乙烯二氧噻吩:聚苯乙烯磺酸盐(PEDOT:PSS)作为最常用的空穴传输层(HTL)材料之一,由于其存在着吸湿性强以及能级与钙钛矿层不匹配等缺点,限制了它的应用。基于此,本文拟采用将左旋多巴(DOPA)和N,N-二甲基亚砜(DMSO)共同掺杂于PEDOT:PSS作为HTL的简单方法制备高性能p-i-n型钙钛矿太阳能电池。研究结果表明,DOPA和DMSO共掺杂PEDOT:PSS可以有效的调节HTL的能级并提高其导电性,器件的能量转化效率由13.35%显著提高到了17.54%。进一步研究发现,相比于未掺杂或单一掺杂的PEDOT:PSS,在DOPA和DMSO共掺杂的PEDOT:PSS上更有利于生长大尺寸、高结晶度的钙钛矿晶体;同时稳态/瞬态荧光和交流阻抗测试表明器件的内部载流子分离和传输更加有效。

In the past decade,perovskite solar cells(Pero-SCs)have attracted a great deal of attention owing to their soaring power conversion efficiency(PCE),up to 22.7%in 2017.In p-i-n type Pero-SCs,one of the most commonly used hole transport layer(HTL)materials is poly(3,4-ethylenedioxythiophene):polystyrenesulfonate(PEDOT:PSS),which possesses a high coverage and an extremely smooth surface.However,the inferior electrical conductivity(or large series resistance)and lower work function(WF)of PEDOT:PSS relative to many other HTL materials limits the open-circuit voltages of Pero-SCs.Furthermore,the hygroscopic property and the acidic nature of PEDOT:PSS can readily cause the degradation of perovskite,and thereby affect the long-term stability of Pero-SCs.The abovementioned disadvantages can hinder the application of PEDOT:PSS in high-performance and stable Pero-SCs;therefore,many efforts have been made to modify PEDOT:PSS to prevent these disadvantages,for instance,adding various organic solvents,surfactants,salts,or acids to PEDOT:PSS as dopants.In this paper,we report a simple codoping method to modify PEDOT:PSS,i.e.,employing L-3,4-dihydroxyphenylalanine(DOPA)and dimethyl sulfoxide(DMSO)as codopants in PEDOT:PSS,and applying it as a HTL in p-i-n type Pero-SCs.Herein,DOPA and DMSO were mixed separately with PEDOT:PSS to obtain HTLs for comparison.The DMSO-doped PEDOT:PSS improved the conductivity of the PEDOT:PSS film,while the DOPA-doped PEDOT:PSS tuned the WF of the PEDOT:PSS film.Hence,codoping of DMSO and DOPA not only allows for a good match of the energy levels between PEDOT:PSS and the perovskite but also leads to an improvement in the conductivity of PEDOT:PSS.The champion PCE of the Pero-SCs increased from 13.35%to 17.54%after DOPA and DMSO were codoped in PEDOT:PSS.Owing to their aligned energy levels and enhanced charge transportation,the detailed photovoltaic parameters were greatly improved.Scanning electron microscope and Xray diffraction were used to characterize the morphological change and crystallinity of the perovskite films.Morphological characterization also revealed that the density of grain boundaries in the perovskite films decreased,which should alleviate the charge recombination occurring in the photoactive layer.Both steady-state photoluminescence(PL)and time-resolved PL characterizations were carried out,and they indicated that nonradiative recombination increased for the perovskite films prepared on the doped PEDOT:PSS films.This result explains the improved short-circuit current density.Electrochemical impedance spectroscopy was employed to determine the resistances of the solar cells.The results are consistent with device performance and that reflected in the PL spectra.