Carboxy Cellulose as Cathode Interfacial Layer for Efficient Organic Solar Cells

Green, biodegradable, and eco-friendly interface materials based on cellulose and its derivatives were prepared for organic solar cells (OSCs). In this work, calcium and two derivatives of cellulose with different carboxy acid groups, denoted as Cellulose-COOH and Cellulose-(COOH)_n, were used as cathode interfacial layers of OSCs, and a blend of the low-band-gap semiconducting polymers thieno[3, 4-b]thiophene/benzodithiophene (PTB7) and [6, 6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) was chosen as the photoactive layer. OSCs were fabricated with a configuration of indium-doped tin oxide (ITO) /poly(3, 4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT: PSS) /PTB7:PC₇₁BM/Ca or Cellulose-COOH or Cellulose-(COOH)_n/Al. As a result, the effect of cellulose-COOH was the best one among them, and the power conversion efficiency (PCE) reached 8.21% for the devices with cathode interfacial layer of Cellulose-COOH, which was better than that of OSCs using calcium as a modifier (PCE=7.95%). The favorable performance is attributed to the reduced work function and improved electron transfer caused by the introduction of carboxy cellulose between the active layer and the electrode. The developed technology shows great potential in accelerating the diversified applications of cellulose and producing cost-effective and eco-friendly interfaces for OSCs.