Enhancement of near-infrared absorption with high fill factor in lead phthalocyanine-based organic solar cells

Abstract

Enhancing the short circuit current (J SC ) by extending the absorption to the near-infrared (NIR) spectrum, which has 50% of the total solar photon flux, is a remaining task in small molecular solar cells. Here, high efficiency NIR absorbing solar cells based on lead phthalocyanine (PbPc) are reported using copper iodide (CuI) as a templating layer to control the crystal structure of PbPc. Devices with CuI inserted between the ITO and PbPc layers exhibit a two times enhancement of the J SC compared to the case in the absence of the CuI layer. This is explained by the increase of crystallinity in the molecules grown on the CuI templating layer, which is investigated via an X-ray diffraction study. Moreover, fill factor is also enhanced to 0.63 from 0.57 due to low series resistance although the additional CuI layer is inserted between the ITO and the PbPc layer. As a result, the corrected power conversion efficiency of 2.5% was obtained, which is the highest one reported up to now among the PbPc based solar cells.

Boosting Photon Harvesting in Organic Solar Cells with Highly Oriented Molecular Crystals via Graphene–Organic Heterointerface

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Especially, it has been well established that the orientation of conjugated organic molecules determines their electrical properties by governing the overlap of π orbitals in the direction of charge transport. [1][2][3][4][5][6][7][8][9][10][11][12][13] For field-effect transistor applications, the molecular planes perpendicular to the substrate is beneficial for the lateral transport of charge carriers through the channel region, which is one of the determinant for the field-effect mobility and resultant device performances.…”

“…15 The energetic states of excitons and exciplexes (or charge-transfer excitons among heterogeneous molecular interfaces) could also be affected by the molecular orientation because of the different orbital overlap among the molecules. 16,17 In this sense, it can be easily inferred that controlling the molecular orientation could be an important strategy to optimizing the device performance of organic optoelectronic devices, especially organic solar cells (OSCs), which could provide an efficient renewable energy source by rapid energy payback time. 18 Moreover, since the small-molecule based OSCs could provide potential advantage over polymer based OSCs due to their greater ease of purifying the materials, the small-molecule based OSCs could be highly feasible for the practical applications and mass-production of the energy devices.…”

Enhanced performance of PbPc photosensitive organic field effect transistors by inserting different-thickness pentacene inducing layers

“…It is known, PbPc molecule has two kinds of crystal structures, i.e., monoclinic and triclinic [17,18] phase has higher crystallinity than the monoclinic [19]. Moreover, PbPc film usually displays two optical absorption peaks in the red and NIR regions, and the NIR absorption of the triclinic phase is stronger than the monoclinic [15]. Therefore, the formation of triclinic phase is a favorable factor for PbPc film to enhance its NIR absorption.…”

“…Similarly, Yin et al [24] reported performance-improved phthalocyanine derivative FETs by inserting a para-quarterphenyl (p-4p) INL. Subsequently, Kim et al [15] displayed a high-efficiency NIR absorbing solar cells based on PbPc by using CuI as an INL. After that, Xue et al [16] proved that a crystalline pentacene INL improves the crystallinity of PbPc film and increases the content of the triclinic phase thereby enhancing the performance of PbPc/C 60 cells.…”

“…To address this problem, two feasible strategies have been proposed and implemented: (i) gate oxide surface modification, such as octadecyltrichlorosilane (OTS) [9], hexamethyldisilizane (HMDS) [10] and etc., are often used to modify the gate oxide surface thus minimizing the carrier trapping at the surface by passivating the hydroxyl bonds on the surface [11], but the passivation effect is severely affected by the preparation technology of modification layer; and (ii) heterojunction structure, it is by organic heterojunction structure that the discrete high-mobility channel layer and the high-absorption photosensitive layer can be integrated in a single device, such structures including planar heterojunction [12], bulk heterojunction [13] and hybrid planar-bulk heterojunction [14]. In addition to these, another simple and effective method is to adopt interfacial inducing layer (INL) [15,16]. As a widely used organic NIR photosensitive material, PbPc, has drawn intense interest in organic solar cells and organic photodetectors.…”