Molecular Doping Efficiency in Organic Semiconductors: Fundamental Principle and Promotion Strategy

Abstract

Molecular doping, a fascinating technique to modulate the electrical property of organic solids by importing additional charges, has been one of the focal points of active research over the last three decades. Due to the potential applications in clean energy and artificial intelligence, molecular doping is experiencing a second golden stage by virtue of its compatibility with solution‐processed organic functional devices. The central challenge at present promoting the doping efficiency. This perspective starts with revisiting the basic concepts in doping process and discusses the recent progress in efficiency improvements. Based on the journey of molecular doping, it is concluded that molecular doping can be as efficient as atomic doping is in inorganic semiconductors; future directions to achieve this goal are shared.

N-doping of nonfullerene bulk-heterojunction organic solar cells strengthens photogeneration and exciton dissociation

“…4,8–10 However, a high doping level in BHJ layers is often undesired since the coulombic potential of dopant counterions can create additional traps and thereby diminish the long-range order of molecular packing, 11,12 which serves as a bottleneck to increasing electrical conductivity and preventing over-high dark carrier density. 13 In principle, n- or p-doping are both feasible in electron acceptors and donors, respectively, yet n-doping in OSCs is remarkably more challenging due to limited candidate dopants, mismatched energy levels and air instability. 4,8…”

“…4,[8][9][10] However, a high doping level in BHJ layers is oen undesired since the coulombic potential of dopant counterions can create additional traps and thereby diminish the long-range order of molecular packing, 11,12 which serves as a bottleneck to increasing electrical conductivity and preventing over-high dark carrier density. 13 In principle, n-or p-doping are both feasible in electron acceptors and donors, respectively, yet n-doping in OSCs is remarkably more challenging due to limited candidate dopants, mismatched energy levels and air instability. 4,8 Since the Zhan group pioneered the design of the rst nonfullerene acceptor (NFA), 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)dithieno[2,3-d:2 0 ,3 0 -d 0 ]-s-indaceno[1,2-b:5,6-b 0 ]dithiophene (ITIC), in 2015, recent years have witnessed unparalleled advances in NFAs and their OSCs (namely, NF-OSCs), thanks to their tunable electronic structures and strong optical absorption in the visible and near-infrared bands compared to fullerene acceptors.…”

“…4,8 While these studies afford a vital guidance for n-doping in NF-OSCs, it would be particularly desirable to obtain more mechanistic understanding. 13 In the rst instance, the light absorption enhancement of the doped active layer is generally described to be a major key to the photocurrent increase, yet the correlation between n-doping and optical absorbance awaits to be clari-ed. 4,8 For another, since it is difficult to control the dopant distribution in the layers prepared by directly introducing dopants into the blend solution, 18,19 the doping effects on exciton generation and diffusion within donor/acceptor (D/A) domains are also noteworthy but far from understood.…”

Molecular Doping Increases the Semitransparent Photovoltaic Performance of Dilute Bulk Heterojunction Film with Discontinuous Polymer Donor Networks

“…Alternatively, molecular doping, which introduces extra holes (p-doping) or electrons (n-doping) via electrostatic induction or certain chemical reaction, has the potential to regulate these electronic defects. [17][18][19][20][21][22] It has been reported that the PCE values of doped OSCs were 17.1%The semitransparent and colorful properties of organic solar cells (OSCs) attract intensive academic interests due to their potential application in building integrated photovoltaics, wearable electronics, and so forth. The most straightforward and effective method to tune these optical properties is varying the componential ratio in the blend film.…”

“…Alternatively, molecular doping, which introduces extra holes (p-doping) or electrons (n-doping) via electrostatic induction or certain chemical reaction, has the potential to regulate these electronic defects. [17][18][19][20][21][22] It has been reported that the PCE values of doped OSCs were 17.1%…”