Embedded surface relief gratings by a simple method to improve absorption and electrical properties of polymer solar...

We demonstrate a simple rubbing hole injection layer (HIL) to form surface relief gratings (SRGs) on the functional layers of polymer solar cells (PSCs). PSCs studied in this work consist of an ITO/PEDOT:PSS(HIL)/P3HT:PCBM(photoactive layer)/LiF/Al structure. SRGs are successfully formed on HIL in an effective rubbing process, and are over printed on the photoactive layer and cathode consequently. These triplet SRGs change the morphologies of interfaces of PSCs, which can increase optical path lengths, interaction between HIL and P3HT chains, and interface areas between electrode and photoactive layer. Both light trapping and electrical improvement are confirmed by theory and experiments, which lead to overall increase in short-circuit current density, fill factor, and power conversion efficiency (PCE) of PSCs. An average PCE of 3.8% is achieved from PSCs with SRGs without thermal annealing. Different from the directly rubbing the donor polymer film, a suitable degree of orientation of P3HT presents a lower dichroic ratio and higher photovoltaic response in our work.