Porphyrin-based thick-film bulk-heterojunction solar cells for indoor light harvesting†
A porphyrin-based donor material P1 is used to fabricate bulk-heterojunction solar cells harvesting room light. P1 consists of a porphyrin ring linked by two ethylrhodanine end caps via phenylene ethynylene bridges. Organic photovoltaic (OPV) cells using P1 as the donor exhibit significantly improved performances under indoor illumination compared to 1 sun conditions. For P1:PC71BM cells, an optimized-PCE of 19.2% was achieved under a 300 lux illumination of a 3000 K LED tube. Besides high PCEs, the porphyrin-based devices also exhibit enhanced OPV performances in thick film regions (∼200 nm) compared to a control BHJ cell using PCDTBT:PC71BM. The thick-film P1-based device shows an overall PCE of 18.2%. The origins of the thickness independent OPV performances were examined, and they can be attributed to the low electronic disorders of these materials when compared to their polymer counterparts.