Abstract
An optimized fabrication of bulk-heterojunction solar cells (BHJ SCs) based on previously reported diketopyrrolopyrrole donor, ethyl-hexylated DPP(TBFu)2, as well as two new DPP(TBFu)2derivatives with ethyl-hexyl acetate and diethyl acetal solubilizing side-chains and PC60BM as an acceptor is demonstrated. Slow gradual annealing of the solar cell causing the effective donor-acceptor reorganization, and as a result higher power conversion efficiency (PCE), is described. By replacing a hole transporting layer PEDOT:PSS with MoO3we obtained higher PCE values as well as higher thermal stability of the anode contact interface. DPP(TBFu)2derivative containing ethyl-hexyl acetate solubilizing side-chains possessed the best as-cast self-assembly and high crystallinity. However, the presence of ethyl-hexyl acetate and diethyl acetal electrophilic side-chains stabilizes HOMO energy of isolated DPP(TBFu)2donors with respect to the ethyl-hexylated one, according to cyclic voltammetry.
Highlights
Polymer and small molecules (SMs) bulkheterojunction (BHJ) organic solar cells (SCs) exceeding 11% power conversion efficiency (PCE) [1] and lifetimes above 1000 hours under continuous illumination [2, 3] attracted particular interest due to their flexibility, color tunability, and predominantly potentially low production cost
It is known that the MoO3 used as hole-selective (transporting) contact (HSC) [26, 27] instead of PEDOT:PSS can improve in some cases PCE of bulk-heterojunction solar cells (BHJ SCs) [28], so we studied its effect in detail, including the thermal stability of the contacts
One of the main achievements of the present paper is the study of the MoO3 anode contact advantages in case of the OSCs based on DPP(TBFU)2, where more thermally stable interface of active layer and anode contact allows using higher annealing temperatures resulting in higher efficiencies in comparison with PEDOT:PSS
Summary
Polymer and small molecules (SMs) bulkheterojunction (BHJ) organic solar cells (SCs) exceeding 11% power conversion efficiency (PCE) [1] and lifetimes above 1000 hours under continuous illumination [2, 3] attracted particular interest due to their flexibility, color tunability, and predominantly potentially low production cost. One of the most promising structural classes of the donors in BHJ SCs is diketopyrrolopyrrole (DPP) derivatives, which show excellent photovoltaic performance as both a part of polymers [7,8,9,10] and dimers [11,12,13], because of a low band gap, enabling them to absorb a large portion of the solar spectrum, as well as an ability to be further functionalized to match the parameters required for the photovoltaic applications. Various aspects of the photovoltaic activity such as hole mobility [25] were understood to the most detailed extent
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