Enhanced Performance in Polymer Solar Cells by Surface Energy Control

Abstract

Enhanced performance of an inverted‐type polymer solar cell is reported by controlling the surface energy of a zinc oxide (ZnO) buffer layer, on which a photoactive layer composed of a polymer:fullerene‐derivative bulk heterojunction is formed. With the approach based on a mixed self‐assembled monolayer, the surface energy of the ZnO buffer layer can be controlled between 40 mN m−1 and 70 mN m−1 with negligible changes in its work function. For the given range of surface energy the power conversion efficiency increases from 3.27% to 3.70% through enhanced photocurrents. The optimized morphology obtained by surface energy control results in the enhanced photocurrent and transmission electron microscopy analysis verifies the correlation between the surface energy and the phase morphology of the bulk heterojunction. These results demonstrate that surface energy control is an effective method for further improving the performance of polymer solar cells, with potentially important implications for other organic devices containing an interface between a blended organic active layer and a buffer or an electrode layer.

Molecular Interlayers in Hybrid Perovskite Solar Cells

“…The simplest interlayers influence active layer morphology by controlling the surface energy and the wetting properties of the substrate. [16] An interesting study into surface energy control of ZnO for organic solar cells was presented by Bulliard et al [16] They used silane molecules with different terminal functional groups to modify the ZnO coated substrate in order to tune the surface energy (30-70 mN m −1 ) without changing the work function. The surface energy was effectively adjusted when different ratios of mixed molecules with hydrophilic (NH 2 ) and hydrophobic terminal groups (CH 3 ) were used.…”

“…[52][53][54] Cells can achieve high energy conversion efficiencies but suffer from relatively low stability when they are subjected to high temperature, a humid atmosphere, UV light or even when a current [16,38] Panels a) and b) are images of a P3HT:PCBM heterojunction on substrates with different surface energies. Panels c) and d) are images of CH 3 NH 3 PbI 3 perovskite layers deposited on substrates with and without 3-aminopropanoic acid interlayers.…”

“…It is worth mentioning that in some situations, the molecules are employed in combination with metal oxides to give a "synergistic effect" for electron or hole extraction. [16,38,41] For example, in a polymer solar cell, a layer of metal oxide is used as an electron blocking layer and a small molecule is used at the same time to tune the work function. [16] Wentao Deng is currently a research assistant in Zhang et al used two perylene diimide derivatives with good conductivity to tune the work function of the electrodes in polymer solar cells.…”

“…[16,38,41] For example, in a polymer solar cell, a layer of metal oxide is used as an electron blocking layer and a small molecule is used at the same time to tune the work function. [16] Wentao Deng is currently a research assistant in Zhang et al used two perylene diimide derivatives with good conductivity to tune the work function of the electrodes in polymer solar cells. [40] Perylene diimide interlayers can effectively reduce the work function of metal electrodes as can be seen in Table 1.…”

Effect of Self-Assembled Monolayer Treated ZnO on the Photovoltaic Properties of Inverted Polymer Solar Cells

“…A layer of 40 nm thick ZnO film was spin-coated on the ITO coated glass and then cured at 300°C for 10 min to partly crystallize the ZnO lm, which is prepared by the literature procedures. 26,27 Self-assembled molecule was deposited on the ZnO lm by spin-coating a 1.0 mg/mL solution of benzoic acid derivative in methanol at 4000 rpm for 60 s. In order to remove physically absorbed molecules, the SAM treated ZnO surface was washed using pure methanol and then dried by the stream of nitrogen. The photoactive layer was formed from 20 mg of P3HT and 20 mg of PC 61 BM blend in 1 mL of o-dichlorobenzene (ODCB) at 600 rpm for 40 s. The sample was then dried in a covered glass petri dish for 1 h. Prior to spin coating, the active solution was ltered through a 0.45 m membrane lter.…”