Abstract
Organic photovoltaic cells (OPVs) have been a hot topic for research during the last decade due to their promising application in relieving energy pressure and environmental problems caused by the increasing combustion of fossil fuels. Much effort has been made toward understanding the photovoltaic mechanism, including evolving chemical structural motifs and designing device structures, leading to a remarkable enhancement of the power conversion efficiency of OPVs from 3% to over 15%. In this brief review, the advanced progress and the state-of-the-art performance of OPVs in very recent years are summarized. Based on several of the latest developed approaches to accurately detect the separation of electron-hole pairs in the femtosecond regime, the theoretical interpretation to exploit the comprehensive mechanistic picture of energy harvesting and charge carrier generation are discussed, especially for OPVs with bulk and multiple heterojunctions. Subsequently, the novel structural designs of the device architecture of OPVs embracing external geometry modification and intrinsic structure decoration are presented. Additionally, some approaches to further increase the efficiency of OPVs are described, including thermotics and dynamics modification methods. Finally, this review highlights the challenges and prospects with the aim of providing a better understanding towards highly efficient OPVs.
Highlights
Photovoltaic (PV) technology, which allows the generation of electricity directly from sunlight, is expected to play a major role in solving the global energy crisis in an environmentally-friendly and sustainable way
organic light-emitting devices (OLEDs) for display and solid state lighting have been commercialized, and in comparison, organic photovoltaic cells (OPVs) has been improved from a fancy concept with less than 1% power conversion efficiency (PCE) to over 10% PCE to meet the requirement of the PV marketplace [13]
When using higher LUMO fullerene, i.e., indene-C60 bisadduct (IC60BA) and indene-C70 bisadduct (IC70BA), the VOC was effectively enhanced from 0.8 V to near 1 V, the JSC and fill factor (FF) obviously decreased, which was ascribed to additional energy loss paths [59]
Summary
Photovoltaic (PV) technology, which allows the generation of electricity directly from sunlight, is expected to play a major role in solving the global energy crisis in an environmentally-friendly and sustainable way. Various exploits in device architecture and processing techniques, as well as further understanding of the OPV functioning mechanism all make contributions toward achieving high PCE. From their very beginning, the OPVs were simple, single-layer devices based on a Schottky diode structure, a pristine polymer and two electrodes, resulting in low PCE [20,21,22]. The short exciton diffusion length requires the thickness of the active layer to be thin enough, which, in turn, impedes light absorption In this case, in 1992, a bulk heterojunction (BHJ) structure was employed to overcome the primary issue in double-layer. Electron transport layer (ETL) will not be discussed here, which play a critical role in OPV performance
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