Simultaneous Passivation of Surface Vacancies and Enhancement in Charge Transfer Property of ZnO Electron Transport Layer for Inverted Organic Solar Cells

Abstract

The design and development of a charge carrier transport material are decisive parameters for controlling the organic solar cell's power conversion efficiency (PCE). ZnO is one of the most suitable electron transport materials used in inverted bulk heterojunction polymer solar cells. However, the solution‐processed ZnO has surface defects, which hinders the power conversation efficiency of the device. Herein, it is designed and demonstrated that the 2D NO2 group functionalized reduced graphene oxide (rGN) sheet coated on top of the 1D ZnO nanoridges not only passivates the surface but also enhances the charge transport property of the electron transport layer (ETL), thereby improving the overall PCE by 31%. Atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and optical measurements reveal that the highly transparent bilayer ZnO/rGN ETL has uniform film formation and, thereby, improved ohmic contact between the cathode and the photoactive layer. Due to the improved electron transport from the photoanode (PTB7‐Th:PC71BM) to the buffer layer, a photoinduced current density of 20.05 mA cm−2 is achieved. This interface modification by rGN can be an effective strategy to passivate the surface and retards the recombination rate to enhance the efficiency of organic photovoltaic cells.

A Light Soaking Free Solution Processable Metal Oxide Cathode Interfacial Layer Enables High Efficiency in Bulk Heterojunction Polymer Solar Cells

“…Moreover, the SCLC method was used to study the influence of heteroatom and graphene on the electron transport properties of the TiO 2 CIL. The electron-only devices were fabricated with a device structure of ITO/TiO 2 or heteroatom and graphene incorporated, and the electron mobility was calculated from the equation − …”

“…The time-resolved photoluminescence (TRPL) measurement is elucidating the charge separation and recombination dynamics in heteroatom, graphene-modified TiO 2 CILs (Supporting Information Figure S7). The defect passivation induced charge transfer is obtained from the TRPL exciton decay lifetime . For TiO 2 , τ 1 (fast decay time constant) and τ 2 (slow decay time constant) values were calculated to be 10.5 and 25.6 ns.…”

“…The defect passivation induced charge transfer is obtained from the TRPL exciton decay lifetime. 38 For TiO 2 , τ 1 (fast decay time constant) and τ 2 (slow decay time constant) values were calculated to be 10.5 and 25.6 ns. Compared with TiO 2 , the lifetime of the charge carrier in TUG-TiO 2 is reduced to 2.15 ns (τ 1 ) and 8.05 ns (τ 2 ).…”

Engineered Cathode Buffer Layers for Highly Efficient Organic Solar Cells: A Review

“…To solve these issues, the further treatment of ZnO has been suggested and it is called passivation of ZnO surface. Pandi et al [140] introduced the reduced graphene oxide (rGN) sheet and it improved the charge transport properties by reducing the surface defects. Similar mechanism has been reported by using triethanolamine and indum (In).…”

“…Pandi et al. [ 140 ] introduced the reduced graphene oxide (rGN) sheet and it improved the charge transport properties by reducing the surface defects. Similar mechanism has been reported by using triethanolamine and indum (In).…”