Polymer solar cells spray coated with non-halogenated solvents

- Environment-friendly non-halogenated solvents were used to spray-coat the active layers.
- Both drying kinetics and charge decay dynamic of spray-processed films were systematically investigated.
- Substrate temperatures have a great effect on the spray-coated film morphology.
- Spray-processed films with randomly textured surface provide a simple and efficient route to increase light absorption.
- Spray-coated ITO-free inverted solar cells processed from non-halogenated solvents were fabricated for the first time.

Using spray-coating technique, we successfully fabricated conventional ITO-based and inverted ITO-free polymer solar cells (PSCs) based on a conjugated polymer poly[2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6] -phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. Environment-friendly non-halogenated solvents were used to process the active layers. The influence of substrate temperatures and processing solvents on the photovoltaic performance of the ITO-based TQ1:PC61BM PSCs was systemically investigated. A higher substrate temperature can accelerate the solvent evaporating rate and afford a micro-textured rougher surface, which efficiently reduced light reflectance and enhanced absorption. Furthermore, finer phase separation was observed when using this high substrate temperature, which led to enhanced photocurrent due to the reduced bimolecular recombination. The device performance of spray-processed PSCs using the non-halogenated solvent mixtures was comparable to that of spray-processed PSCs using the halogenated o-dichlorobenzene (oDCB), which demonstrates that the non-halogenated solvents are very promising in spray-processed PSCs. This work sheds new light on developing efficient roll-to-roll compatible spray-coated PSCs with environment-friendly solvents.