Abstract
Over the last four years, tremendous progress has occurred in the field of organic photovoltaics (OPVs) and the champion power conversion efficiency (PCE) under AM1.5G conditions, as certified by the National Renewable Energy Laboratory (NREL), is currently 18.2%. However, these champion state-of-the-art devices were fabricated at lab-scale using highly toxic halogenated solvents which are harmful to human health and to the environment. The transition of OPVs from the lab to large-scale production and commercialization requires the transition from halogenated-solvent-processing to green-solvent-processing without compromising the device’s performance. This review focuses on the most recent research efforts, performed since the year 2018 onwards, in the development of green-solvent-processable OPVs and discusses the three main strategies that are being pursued to achieve the proposed goal, namely, (i) molecular engineering of novel donors and acceptors, (ii) solvent selection, and (iii) nanoparticle ink technology.
Highlights
Organic photovoltaics [1] have undergone rapid development over the last few years largely due to the synthesis and testing of new polymer donors [2,3] and new non-fullerene acceptors [4,5,6]
Small organic photovoltaics (OPVs) cells based on the photoactive layers (PALs) PM7:IT-4F and processed from toluene achieved an impressive power conversion efficiency (PCE) of 13.1%, much higher than the PCE of 5.8% exhibited by similar PBDBT:IT-4F devices processed from toluene
Whilst the champion efficiencies of lab-scale OPV devices have witnessed a rapid increase in recent years, the majority of these champions devices were processed from halogenated and aromatic solvents
Summary
Organic photovoltaics [1] have undergone rapid development over the last few years largely due to the synthesis and testing of new polymer donors [2,3] and new non-fullerene acceptors [4,5,6]. The second strategy, here named, rational solvent selection or solvent selection, consists in finding suitable green solvents, either single (solvency) or mixed (co-solvency), for well-established donor: acceptor pairs, based either on a simple trial-and-error approach or on a more systematic testing using Hansen solubility parameters concepts as an important guide. This strategy has the limitation that it may not be possible to find appropriate solvents or solvent combinations for many high-efficiency donor:acceptor pairs. The record efficiency using a halogenated solvent (closed black circle) is shown for reference
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