Fabricating High Performance, Donor–Acceptor Copolymer Solar Cells by Spray‐Coating in Air

Abstract

We report the fabrication of high performance organic solar cells by spray‐coating the photoactive layer in air. The photovoltaic blends consist of a blend of carbazole and benzothiadiazole based donor–acceptor copolymers and the fullerene derivative PC70BM. Here, we formulate a number of photovoltaic inks using a range of solvent systems that we show can all be deposited by spray casting. We use a range of techniques to characterize the structure of such films, and show that spray‐cast films have comparable surface roughness to spin‐cast films and that vertical stratification that occurs during film drying reduces the concentration of PCBM towards the underlying PEDOT:PSS interface. We also show that the active layer thickness and the drying kinetics can be tuned through control of the substrate temperature. High power conversion efficiencies of 4.3%, 4.5% and 4.6% were obtained for solar cells made from a blend of PC70BM with the carbazole‐based co‐polymers PCDTBT, P2 and P1. By applying a low temperature anneal after the deposition of the cathode, the efficiency of spray‐cast solar‐cells based on a P2:PC70BM blend is increased to 5.0%. Spray coating holds significant promise as a technique capable of fabricating large‐area, high performance organic solar cells in air.

Impact of solution phase behaviour and external fields on thin film morphology: PCBM and RRa-P3HT model system

“…The importance of the drying pathway has been recognised by several authors and has been found to considerably impact performances. [22][23][24]…”

High performance airbrush spray coated organic solar cells via tuning the surface tension and saturated vapor pressure of different ternary solvent systems

“…Recently, the state-of-arts single junction OSCs with power conversion efficiency (PCE) approaching 9-10% have been achieved via interfacial engineering [5], device optimization [6] and rational material synthesis, e.g., p-type polymers PTB7 [7], PTB7-Th [8], PPDT2FBT [9] and PffBT4T-2OD [10]. However, the above mentioned OSCs are all fabricated based on conventional spin coating method, which is not capable of large-scale fabrication due to its significant waste of materials and limitation on the rigid substrates [11][12][13][14]. Until now, a variety of alternative deposition methods have been emerged including roll-to-roll [15], blade coating [16] and ink-jet printing [17] et al Although a large volume of researches using these techniques have been devoted in maintaining the PCE as high as those based on spin coating, the obvious declines of PCE could be observed for most of bulk heterojunction (BHJ) systems, e.g., P3HT:PC 61 BM and PTB7:PC 71 BM systems [18][19][20][21][22][23][24][25].…”

Fabricating high performance conventional and inverted polymer solar cells by spray coating in air

“…In contrast, spray coating has been used in the fabrication of OPVs and is compatible with large area processing over flexible substrates. [11][12][13][14][15] Notably, most work on the development of spray cast…”

“…[16] More recent work has however explored spray-cast blends of amorphous donor-acceptor co-polymers with fullerene-derivative electron acceptors, with improved device performance demonstrated. [11,13,17,18] Spray-coating has also been used to deposit the various charge transporting layers used in OPV devices. [19] In single junction OPV device based on a conventional architecture, the active layer is deposited onto a hole-transporting layer.…”