The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications

Abstract

Organic semiconductors require an energetic offset in order to photogenerate free charge carriers efficiently, owing to their inability to effectively screen charges. This is vitally important in order to achieve high power conversion efficiencies in organic solar cells. Early heterojunction‐based solar cells were limited to relatively modest efficiencies (<4%) owing to limitations such as poor exciton dissociation, limited photon harvesting, and high recombination losses. The development of the bulk heterojunction (BHJ) has significantly overcome these issues, resulting in dramatic improvements in organic photovoltaic performance, now exceeding 18% power conversion efficiencies. Here, the design and engineering strategies used to develop the optimal bulk heterojunction for solar‐cell, photodetector, and photocatalytic applications are discussed. Additionally, the thermodynamic driving forces in the creation and stability of the bulk heterojunction are presented, along with underlying photophysics in these blends. Finally, new opportunities to apply the knowledge accrued from BHJ solar cells to generate free charges for use in promising new applications are discussed.

Face‐to‐Face Growth of Wafer‐Scale 2D Semiconducting MOF Films on Dielectric Substrates

“…[ 41 ] Thus, a bulk heterojunction with the appropriate energy level matching significantly overcame the exciton recombination and improved device performance. [ 42 ] 2D MOF films are a relatively emergent porous material and may become a promising candidate for application in new types of BHJ photoelectric devices, such as photodetectors, solar cells, artificial optoelectronic synapses, or simulated retinas.…”

Challenges to the Success of Commercial Organic Photovoltaic Products

“…Despite the advantages, mixing two or more components presents challenges to achieve an optimum morphology. [ 17 ] In fact, this usually involves a trial‐and‐error approach and finding a relationship between solar cell efficiency, microstructure, and thin‐film formation kinetics has been challenging. The Flory–Huggins interaction parameter has been reported as a powerful method to correlate the device performance with phase purity and amorphous–amorphous phase diagrams.…”

“…Such properties led to expectations that bulk heterojunction (BHJ) OPVs might be able to compete with their silicon‐based counterparts at some point. [ 17 ] However, significant emphasis has been placed on the production of high‐grade c‐Si in recent years, drastically driving down its cost, as dictated by Swanson's law. [ 18 ] As such, emerging photovoltaic technologies, including OPV, have struggled to compete with silicon on the basis of levelized cost of electricity, with recent costs of c‐Si photovoltaics estimated at 0.30 $ W p −1 .…”

Push–pull thiophene-based small molecules with donor and acceptor units of varying strength for photovoltaic application: beyond P3HT and PCBM

“…The exploration of novel organic semiconductive materials for the development of bulk heterojunction (BHJ) solar cells has led to considerable progress in device performance in the past years. [1][2][3] The careful design of chemical structures, which takes advantage of the input provided by the continuous effort of synthetic chemists, together with a better understanding of the relationship between structure, properties, and performance are driving the development of increasingly high-performing organic photovoltaic materials. [4][5][6][7] Indeed, power conversion efficiencies (PCEs) of organic solar cells are now above 18%, confirming the role of BHJs as a promising technology for future clean energy supply.…”