Ultrathin Organic Solar Cells with a Power Conversion Efficiency of Over ≈13.0%, Based on the Spatial Corrugation of the Metal Electrode-Cathode Fabry-Perot Cavity.

Sungjun In,Namkyoo Park

doi:10.1002/advs.201700900

Abstract

The application of nanophotonic structures for organic solar cells (OSCs) is quite popular and successful, and has led to increased optical absorption, better spectral overlap with solar irradiances, and improved charge collection. Significant improvements in the power conversion efficiency (PCE) have also been reported, exceeding 11%. Nonetheless, with the given material properties of OSCs with low optical absorption, narrow spectrum, short transport length of carriers, and nonuniform photocarrier generations resulting from the nanophotonic structure, the PCE of single‐junction OSCs has been stagnant over the past few years, at a barrier of 12%. Here, an ultrathin inverted OSC structure with the highest efficiency of ≈13.0%, while being made from widely used organic materials, is demonstrated. By introducing a smooth spatial corrugation to the vertical plasmonic cavity enclosing the active layer, in‐plane propagation modes and hybridized Fabry–Perot cavity modes inside the corrugated cavity are derived to achieve an ultralow Q, uniform coverage of optical absorption, in addition to uniform photocarrier generation and transport. As the first demonstration of ultra‐broadband absorption with the introduction of spatial corrugation to the ultrathin metal film electrode–cathode Fabry–Perot cavity, future applications of the same concept in other light‐harvesting devices utilizing different materials and structures are expected.

Highlights

Quite popular and successful, and has led to increased optical absorption, and solution fabrication method[13] better spectral overlap with solar irradiances, and improved charge collection
By introducing a smooth spatial corrugation to the active layer cavity of the UTMFelectrode OSC, without any penalty to electrical transports, we derive a strong multipeak in-plane plasmonic propagation modes in addition to the broadening of the Fabry–Perot cavity modes in the ultrathin metal film (UTMF)-electrode OSC: in order to achieve highly uniform (>85%) and ultralow Q (330–775 nm) absorption, which provide near-perfect spectral overlap to the ultrathin (120 nm) PBDTT-FTT:PC71BM active layer
The highest performance of an organic solar cell of ≈13.0% power conversion efficiency (PCE) was numerically demonstrated by identifying the limitation of conventional UTMF OSC through optical–electrical multiphysics analysis and introducing a corrugated cavity structure which perfects the spectral engineering over the optical absorption of the ultrathin PBDTT-F-TT:PC71BM active layer

Summary

Introduction

Current reports repeatedly show a significant reduction in the fill factors (FF) of nanophotonic structure-based OSCs (e.g., plasmonic nanograting,[14] bumped-structure,[15] and nanoparticle[16]), despite their improved PCE. Working on a simple structure of ultrathin metal film (UTMF)-electrode OSC by employing the optical–electrical multiphysics analysis, we reveal that it is the spectral engineering, perfecting the absorption band of the active layer, not the (electrical) mobility, which defines the present device performances bottleneck of OSC. By introducing a smooth spatial corrugation to the active layer cavity of the UTMFelectrode OSC, without any penalty to electrical transports, we derive a strong multipeak in-plane plasmonic propagation modes in addition to the broadening of the Fabry–Perot cavity modes in the UTMF-electrode OSC: in order to achieve highly uniform (>85%) and ultralow Q (330–775 nm) absorption, which provide near-perfect spectral overlap to the ultrathin (120 nm) PBDTT-FTT:PC71BM active layer. Detailed analysis is carried out on the influence of the corrugated cavity to the optical field hybridization, exciton generation rate, charge carrier collection efficiency, and electrical conversion efficiency, in order to provide deeper insight into the origin of full-visible optical absorption, and to enlighten a systematic pathway in the tuning of electrical performance of OSCs

Performance Analysis of Reference OSC

Performance Analysis of Proposed OSC

Conclusion

Experimental Section

Conflict of Interest