Fullerene-based Schottky-junction organic solar cells: a brief review

Abstract

Recent advances in fullerene-based Schottky organic solar cells (OSCs) are presented, with a focus on the current understanding of device physics. Fullerene-based Schottky OSCs attain high open-circuit voltages due to the n-type Schottky junction formed between fullerene and an adjacent high work function anode. Small concentrations of donor material doped into the fullerene matrix serve as efficient exciton dissociation and hole transport agents that can substantially bolster short-circuit currents and fill factors. As a consequence, fullerene-based Schottky OSCs have been demonstrated to provide some of the highest-performance vacuum-deposited small molecule OSCs, with power conversion efficiencies up to 8.1%. Fullerene-based Schottky OSCs constructed using different donor materials and varying cathode buffer layers, as studied by a number of different research groups, are presented. To elucidate the differences between Schottky OSCs and more traditional bulk-heterojunction OSCs, we discuss the photophysics of fullerenes, the role of the donor material, and charge transport in low donor concentration active layers. Fullerene-based Schottky OSCs possess considerable advantages because they can reach high efficiencies with a simple structure using readily available and cost-effective materials. The impact and applicability of the Schottky device architecture on the field of organic photovoltaics at large are discussed. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

High‐Efficiency Fullerene Solar Cells Enabled by a Spontaneously Formed Mesostructured CuSCN‐Nanowire Heterointerface

“…In contrast, more significant advancements have been made using the so‐called Schottky junction fullerene solar cells, in which small concentrations, usually around 5%, of donor materials are incorporated into the fullerene matrix, which acts as the main absorber. Such cell architectures have shown to exhibit high V OC of over 1 V, and efficiencies of up to 6% . The importance of these cells cannot be understated; fullerenes have been the prototypical 3D semiconductor with a molecular symmetry that is unmatched by any other molecular semiconducting material, and have been synonymous with the rise of the third generation photovoltaics in the form of electron acceptors.…”

Charge Carrier Transport and Generation via Trap-Mediated Optical Release in Organic Semiconductor Devices

“…Optical release may thus present a key to overcome the large losses caused by nonradiative CT state recombination limiting V oc in organic solar cells [5,32]. Finally, apart from the high V oc typically observed in low-donor-content BHJs [17][18][19]41], independent of the donor HOMO, optical release of holes also explains how holes are able to be collected in devices or domains with ultralow donor concentrations. We emphasize that this type of optical release is expected to occur whenever a significant fraction of (donor) sites is occupied (by holes), e.g., at high enough intensities.…”

Origin of Hole Transport in Small Molecule Dilute Donor Solar Cells

“…[ 12 ] High V oc are attributed to the formation of a Schottky barrier between the fullerene matrix and a high work function anode. [ 15 ] In addition, reduced recombination [ 16 ] and ideal morphology at the extraction layers [ 17 ] can further reduce the V oc losses in dilute donor OSCs.…”