All-in-one solar cell: Stable, light-soaking free, solution processed and efficient diketopyrrolopyrrole based small molecule inverted organic solar cells

•First report of DPP based inverted organic solar cell with novel transport layers.•Stable for more than 1000 h even without encapsulation.•Light-soaking free inverted organic solar cells were fabricated.•All-solution-processed transport layers using modified PEDOT:PSS and F-TiOx.•Extensive study on degradation behavior in various exposure conditions.

Organic solar cells (OSC) based on diketopyrrolopyrrole (DPP) small molecule have achieved relatively high efficiency (7%) in recent times. 2,5-di(2-ethylhexyl)-3,6-bis-(5″-n-hexyl-[2,2′,5′,2″]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH) is the workhorse material for small molecule OSC as it has good solution-processing capability. However, there was no previous report on improving the device stability in inverted organic solar cells (IOSC) by using this material. Furthermore, the degradation and light-soaking behavior of this material in IOSC are also not well-addressed. In this work, we have fabricated a stable, light-soaking free, solution-processed and efficient SMDPPEH:PC61BM based IOSC for the first time. Fluorosurfactant modified PEDOT:PSS and fluorinated TiOx (F-TiOx) transport layers were used to circumvent the inherent processability and light-soaking issues. An exclusive study on the device stability and light-soaking characteristics were also carried out for the first time. The final device provides the following merits: (i) comparable material stability to P3HT polymer, suggesting a potential for further development of DPP materials for high-efficiency devices; (ii) F-TiOx can be used universally to fabricate a light-soaking free device with a wide range of photoactive materials from polymers to small molecules and; (iii) higher device efficiency compared to the non-inverted counterpart were obtained when the modified transport layers were used.

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