Optimization of tail state Urbach energy enables efficient organic solar cells and perovskite/organic tandem solar cells

Tail state Urbach energy caused by the molecular disorder and stacking plays a crucial role for obtaining efficient organic solar cells (OSCs). Herein, we proposed a theoretical and experimental method to adjust the Urbach energy (E-U) of organic photoactive materials. Simulation results show that the E-U of 32 meV for PM6:Y6-based single junction (SJ) OSCs can enhance J(sc) and FF significantly, and thus achieving a high photovoltaic conversion efficiency (PCE) of 18.03%. Interestingly, further decreasing E-U within a certain range cannot increase device efficiency obviously, and E-U cannot be close to 0 meV in consideration of the molecule disorder of organic material. Under the guidance of theoretical design, the ternary component IEICO-4F was introduced to optimize E-U Experimental results show that the optimized EU is obtained upon introducing of IEICO-4F, and a championed PCE of 16.61% is achieved when E-U is about 25.80 meV for SJ-OSCs. Tandem solar cells (TSCs) reach an experimental PCE of 18.57% when E-U is about 27.46 meV, which facilitates current matching between the front and rear sub-cells.