Importance of structural hinderance in performance–stability equilibrium of organic photovoltaics

Abstract

Power conversion efficiency and long-term stability are two critical metrics for evaluating the commercial potential of organic photovoltaics. Although the field has witnessed a rapid progress of efficiency towards 19%, the intrinsic trade-off between efficiency and stability is still a challenging issue for bulk-heterojunction cells due to the very delicate crystallization dynamics of organic species. Herein, we developed a class of non-fullerene acceptors with varied side groups as an alternative to aliphatic chains. Among them, the acceptors with conjugated side groups show larger side-group torsion and more twisted backbone, however, they can deliver an efficiency as high as 18.3% in xylene-processed cells, which is among the highest values reported for non-halogenated solvent processed cells. Meanwhile, decent thermal/photo stability is realized for these acceptors containing conjugated side groups. Through the investigation of the geometry–performance–stability relationship, we highlight the importance of side-group steric hinderance of acceptors in achieving combined high-performance, stable, and eco-friendly organic photovoltaics.

Open-Shell Donors and Closed-Shell Acceptors in Organic Solar Cells

“…Moreover, fine tailoring of the molecular structure will effectively modulate the radical characters of donors/acceptors, which can be demonstrated by the obvious changes in chemical/physical properties in OSCs. It will be of great importance to achieve high-performance near-infrared emitters with excellent photovoltaic device performance and stability. − Our studies provided a novel and important guideline for the design of donors and acceptors in OSCs.…”

A Large Area Organic Solar Module with Non‐Halogen Solvent Treatment, High Efficiency, and Decent Stability

“…Compared with the good photostability, the relatively low thermal stability of the module might come from the less densely packing of acceptor CH7 with the large and long branched aliphatic side chains. [46] In contrast, in view of the promising application for semitransparent OSCs as power-generating widows in building-integrated photovoltaics, green-house, etc., [26,50] we fabricated a semitransparent module based on the above active layer with an ultrathin transparent Ag electrode and MoO 3 anti-reflective layer (Figure 4e). After optimization, the semitransparent module exhibits a PCE of 9.69% with an average visible transmittance (AVT) 27.5% (Figure 4f ).…”

“…To date, only several prototype devices processed with non-halogen solvents were reported with efficiencies of over 17%. [14,[41][42][43][44][45][46] To our knowledge, only two cases with efficiencies over 14% were achieved for non-halogen solventprocessed modules. [14,15] From the perspective of the application, it is necessary for a module that simultaneously shows high efficiency, good stability, and green solvents treatment.…”

“…To date, only several prototype devices processed with non‐halogen solvents were reported with efficiencies of over 17%. [ 14,41–46 ] To our knowledge, only two cases with efficiencies over 14% were achieved for non‐halogen solvent‐processed modules. [ 14,15 ]…”

Nonhalogenated Solution‐Processed Donor‐Dispersed Planar Heterojunction Organic Solar Cells with Enhanced Homogeneity in Vertical Phase Separation

“…To increase the commercialization viability of OPVs, using nonhalogenated solvents (NHS) to process OPVs toward high photovoltaic efficiencies has received increased attention. [30][31][32] In this aspect, while visible progress in the efficiency has been achieved, NHS-based OPVs are yet underperforming their device counterparts prepared with halogenated solvents. [33][34][35] This performance gap can be related to the nonoptimal morphology of Q-PHJ (or BHJ) films processed with NHS such that the exciton diffusion length and/or geminate recombination are negatively affected.…”