In this work we report on the eco-friendly processing of PBDTTPD:PC71BM organic solar cells using water-based nanoparticle (NP) dispersions. The polymer:fullerene NPs are prepared using the miniemulsion-solvent evaporation method, despite employing high-boiling solvents. Polymer solar cells are fabricated from these blend NPs and the device characteristics are studied in function of annealing time and temperature. The photoactive layer formation is carefully analyzed using atomic force microscopy (AFM). Annealing for longer times significantly increases the power conversion efficiency (PCE), up to 3.8%, the highest value reported for surfactant based NP solar cells. Our work shows that the low bandgap polymer PBDTTPD has the ability to afford reasonable efficiencies in NP solar cells in combination with PC71BM and paves the way to a truly eco-friendly processing of organic photovoltaics (OPVs). (C) 2016 Elsevier B.V. All rights reserved. ; The authors acknowledge financial support by Hasselt University (BOF), the Research Foundation Flanders (FWO) (project G.0415.14N), and IAP 7/05 project FS2 (Functional Supramolecular systems), granted by the Science Policy Office of the Belgian Federal Government (BELSPO).
The power conversion efficiency of halide perovskite solar cells is heavily dependent on the perovskite layer being sufficiently smooth and pinhole-free. It has been shown that these features can be obtained even when starting out from rough and discontinuous perovskite film by briefly exposing the film to methylamine (MA) vapor. The exact underlying physical mechanisms of this phenomenon are, however, still unclear. By investigating smooth, MA treated films based on very rough and discontinuous reference films of methylammonium triiode (MAPbI3) and considering their morphology, crystalline features, local conductive properties, and charge carrier lifetime, we unraveled the relation between their characteristic physical qualities and their performance in corresponding solar cells. We discovered that the extensive improvement in photovoltaic performance upon MA treatment is a consequence of the induced morphological enhancement of the perovskite layer together with improved electron injection into TiO2, which in fact compensates for an otherwise compromised bulk electronic quality simultaneously caused by the MA treatment. ; This work was financially supported by BOF (Hasselt University) and the Research Fund Flanders (FWO). B.C. is a postdoctoral research fellow of the FWO. A.B. is financially supported by FWO and Imec. J.V. and N.G. acknowledge funding from GOA project "Solarpaint" of the University of Antwerp and FWO project G.0044.13N "Charge ordering". The Qu-Ant-EM microscope used for this study was partly funded by the Hercules fund from the Flemish Government. The authors thank Tim Vangerven for Urbach energy determination and Johnny Baccus and Jan Mertens for technical support.
Three extended molecular chromophores, differing in their central acceptor moiety and specifically designed as electron donor components for small molecule organic solar cells, are synthesized via a two-fold-C-H arylation protocol. Upon removal of the side products inherent to the applied direct (hetero) arylation procedure, a record power conversion efficiency of 5.1% is achieved. ; We acknowledge financial support from the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2), the Agency for Innovation by Science and Technology in Flanders (IWT; PhD grants J. Brebels and T. Vangerven) and the Research Programme of the Research Foundation - Flanders (FWO; M.ERA-NET project RADESOL and projects G.0415.14N/G.0B67.15N).
Conjugated polymers and small molecules based on alternating electron-donating (D) and electronaccepting (A) building blocks have led to state-of-the-art organic solar cell materials governing efficiencies beyond 10%. Unfortunately, the connection of D and A building blocks via cross-coupling reactions does not always proceed as planned, which can result in the generation of side products containing D-D or A-A homocoupling motifs. Previous studies have reported a reduced performance in polymer and small molecule solar cells when such defect structures are present. A general consensus on the impact of homocouplings on device performance is, however, still lacking as is a profound understanding of the underlying causes of the device deterioration. For differentiating the combined effect of molecular weight and homocouplings in polymer solar cells, a systematic study on a small molecule system (DTS(FBBTh2)2) is presented. The impact of homocouplings on nanomorphology, thermal, and electro-optical properties is investigated. It is demonstrated that small quantities of homocouplings (<10%) already lead to suboptimal device performance, as this strongly impacts the molecular packing and electronic properties of the photoactive layer. These results highlight the importance of material purity and pinpoint homocoupling defects as one of the most probable reasons for batch-to-batch variations. ; The authors thank Hasselt University and the Research Foundation Flanders (FWO) for financial support. The collaboration between Hasselt and Mons is supported by the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2). T.V. and M.D. acknowledge the Agency for Innovation by Science and Technology in Flanders (IWT) for their Ph.D. grants. K.V. and J.B. thank the German Federal Ministry for Education and Research (BMBF) for funding through the InnoProfille project "Organische p-i-n Bauelemente 2.2". The M-ERA.NET project "RADESOL" is funded under the EU Seventh Framework Programme (FP7/2007-2013) Grant 234648/O70. J.W.A. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 681881). The authors further acknowledge Huguette Penxten for the CV measurements. The research in Mons is also supported by FNRS-FRFC and the European Commission/Walloon Region (FEDER−BIORGEL project). D.B. is an FNRS Research Director. The authors finally acknowledge TA Instruments for the RHC equipment.
