Abstract
Organic polymer solar cells (PSCs) have attracted increasing attention due to light weight, low cost, flexibility and roll-to-roll manufacturing. However, the limited light harvest range of the photoactive layer greatly restrains the power conversion efficiency (PCE) enhancement. In order to expand the light absorption range and further enhance the PCE of the PSCs, tandem structures have been designed and demonstrated. In tandem solar cell, the intermediate layer (IML) plays a critical role in physically and electrically connection of the two subcells. Herein, we apply titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD) as both electrode modification layer and intermediate layer to investigate the feasibility in inverted tandem polymer solar cells. The same photoactive layers of PTB7-Th:PC71BM are adopted in both front and rear subcells to simplify the evaluation of effectiveness of TIPD layer in tandem structures. By modulating the treatment condition of IML and the thickness of photoactive layer, efficient inverted tandem PSCs have been achieved with minimized voltage loss and excellent charge transportation, giving a best V-oc of 1.54 V, which is almost two times that of the single bulk heterojunction (BHJ)-PSC (0.78 V) and an enhanced PCE up to 8.11%.