Synergic Interface and Optical Engineering for High-Performance Semitransparent Polymer Solar Cells

In this study the thickness of the PTB7-Th: PC71BM bulk heterojunction (BHJ) film and the PF3N-2TNDI electron transport layer (ETL) is systematically tuned to achieve polymer solar cells (PSCs) with optimized power conversion efficiency (PCE) of over 9% when an ultrathin BHJ of 50 nm is used. Optical modeling suggests that the high PCE is attributed to the optical spacer effect from the ETL, which not only maximizes the optical field within the BHJ film but also facilitates the formation of a more homogeneously distributed charge generation profile across the BHJ film. Experimentally it is further proved that the extra photocurrent produced at the PTB7-Th/PF3N-2TNDI interface also contributes to the improved performance. Taking advantage of this high performance thin film device structure, one step further is taken to fabricate semitransparent PSCs (ST-PSCs) by using an ultrathin transparent Ag cathode to replace the thick Ag mirror cathode, yielding a series of high performance ST-PSCs with PCEs over 6% and average visible transmittance between 20% and 30%. These ST-PSCs also possess remarkable transparency color perception and rendering properties, which are state-of-the-art and fulfill the performance criteria for potential use as power-generating windows in near future.