All-polymer solar cells with bulk heterojunction nanolayers of chemically doped electron-donating and electron-accepting polymers

Abstract

We report the improved performance of all-polymer solar cells with bulk heterojunction nanolayers of an electron-donating polymer (poly(3-hexylthiophene) (P3HT)) and an electron-accepting polymer (poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT)), which were both doped with 4-ethylbenzenesulfonic acid (EBSA). To choose the doping ratio of P3HT for all-polymer solar cells, various EBSA doping ratios (0, 1, 3, 5, 10, 20 wt%) were tested by employing optical absorption spectroscopy, photoluminescence spectroscopy, photoelectron yield spectroscopy, and space-charge-limited current (SCLC) mobility measurement. The doping reaction of P3HT with EBSA was followed by observing the colour change in solutions. The final doping ratio for P3HT was chosen as 1 wt% from the best hole mobility measured in the thickness direction, while that for F8BT was fixed as 10 wt% (F8BT-EBSA). The polymer:polymer solar cells with bulk heterojunction nanolayers of P3HT-EBSA (EBSA-doped P3HT) and F8BT-EBSA (EBSA-doped F8BT) showed greatly improved short circuit current density (J(SC)) and open circuit voltage (V(OC)), compared to the undoped solar cells. As a result, the power conversion efficiency (PCE) was enhanced by ca. 300% for the 6 : 4 (P3HT-EBSA : F8BT-EBSA) composition and ca. 400% for the 8 : 2 composition. The synchrotron-radiation grazing incidence angle X-ray diffraction (GIXD) measurement revealed that the crystallinity of the doped nanolayers significantly increased by EBSA doping owing to the formation of advanced phase segregation morphology, as supported by the surface morphology change measured by atomic force microscopy. Thus the improved PCE can be attributed to the enhanced charge transport by the formation of permanent charges and better charge percolation paths by EBSA doping.

On the spatial inhomogeneity of charge generation and collection in inverted all polymer solar cells

“…1) are in agreement with the typical F8BT and rrP3HT ones. 18,20 Also, the presented PL spectrum of the blend film is comparable to the previously reported rrP3HT:F8BT PL spectra, 21,22 for the same relative concentration to the one used in our manuscript.…”

Supramolecular Approaches to Nanoscale Morphological Control in Organic Solar Cells

“…In contrast with the typical edge-on orientation of P3HT in organic solar cell active layers [ 126 , 127 , 128 , 129 ], the P3HT block of the copolymer exhibited a preferential face-on orientation, i.e ., with the molecular plane nearly parallel to the substrate. It was hypothesized that the preferred orientation of the P3HT resulted from the interaction of the PFTBT with the underlying poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) hole transport layer [ 130 ] which led to a face-on orientation for the PFTBT; since the P3HT was linked to the PFTBT, it adopted a similar orientation [ 125 ]. A face-on molecular orientation provides efficient out-of-plane charge transport, along the molecular stacking direction, to the charge collecting electrodes [ 38 , 39 , 53 , 54 , 55 , 56 ].…”

Decreased domain size and improved crystallinity by adjusting solvent–polymer interaction parameters in all‐polymer solar cells

“…It is generally believed that the morphology of the active layer in PSCs plays a crucial role in determining the device performance . The ideal morphology should possess interconnected phases with a typical length scale of ∼ 10 nm, which can ensure the efficient exciton dissociation and charge collection .…”