Abstract
Polymer solar cells (PSCs) are greatly influenced by both the vertical concentration gradient in the active layer and the quality of the various interfaces. To achieve vertical concentration gradients in inverted PSCs, a sequential deposition approach is necessary. However, a direct approach to sequential deposition by spin-coating results in partial dissolution of the underlying layers which decreases the control over the process and results in not well-defined interfaces. Here, we demonstrate that by using a transfer-printing process based on polydimethylsiloxane (PDMS) stamps we can obtain increased control over the thickness of the various layers while at the same time increasing the quality of the interfaces and the overall concentration gradient within the active layer of PSCs prepared in air. To optimize the process and understand the influence of various interlayers, our approach is based on surface free energy, spreading parameters and work of adhesion calculations. The key parameter presented here is the insertion of high quality hole transporting and electron transporting layers, respectively above and underneath the active layer of the inverted structure PSC which not only facilitates the transfer process but also induces the adequate vertical concentration gradient in the device to facilitate charge extraction. The resulting non-encapsulated devices (active layer prepared in air) demonstrate over 40% increase in power conversion efficiency with respect to the reference spin-coated inverted PSCs.
Highlights
Polymer solar cells (PSCs) [1,2,3,4,5] have been developed over the past decade and reach power conversion efficiencies (PCE) overcoming the milestone value of 10%.[6,7,8,9,10,11,12] In order to become a realistic alternative to the state-of-the-art silicon solar cells, developers of PSCs are required to either remarkably increase their photovoltaic performances or to considerably reduce the cost of production.[13]
The devices prepared using the transfer process exhibit an average increase of 40% with respect to the reference spin-coated cells, demonstrating that PCE up to 2.4% can be obtained with P3HT:PCBM active layers processed entirely in air
Using theoretical calculations correlated with practical experiments, we have introduced an efficient method to transfer PEDOT:PSS/active layers from PDMS stamps to the underlying substrates
Summary
Polymer solar cells (PSCs) [1,2,3,4,5] have been developed over the past decade and reach power conversion efficiencies (PCE) overcoming the milestone value of 10%.[6,7,8,9,10,11,12] In order to become a realistic alternative to the state-of-the-art silicon solar cells, developers of PSCs are required to either remarkably increase their photovoltaic performances or to considerably reduce the cost of production.[13]. (3) The optimized conditions for transfer-printing correspond to the ideal device architectures in inverted PSCs. As PEDOT:PSS and PCBM can act as hole only and electron only layers respectively in an inverted PSC architecture, the results presented here demonstrate three key surface and interface aspects to successfully fabricate inverted PSCs with a vertical concentration gradient. (3) The optimized conditions for transfer-printing correspond to the ideal device architectures in inverted PSCs This method results in the fabrication of sequentially deposited multilayer PSC active layers and provides means to fabricate a homogeneous PEDOT:PSS layer between the active layer and the metal electrode in inverted PSCs. The devices prepared using the transfer process exhibit an average increase of 40% with respect to the reference spin-coated cells, demonstrating that PCE up to 2.4% can be obtained with P3HT:PCBM active layers processed entirely in air
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