Studies on One-Step-Synthesized Hydrated Vanadium Pentoxide for Efficient Hole Transport in Organic Photovoltaics

Abstract

Recently, the use of nonfullerene acceptors (NFA) and high‐mobility less corrosive hole transport materials in organic photovoltaics (OPV) has led to the power conversion efficiency (PCE) values ≈15% for single‐junction and ≈18% for tandem‐junction cells. Herein, the development of hydrated vanadium pentoxide (HVO) films with excellent hole transport/electron blocking capabilities via a facile synthetic route with low environmental footprint is reported. Polymer solar cells (PSC) are fabricated with both standard and inverted polymer solar cell (IPSC) architectures using the standard bulk heterojunction blends P3HT:PC61BM and low‐bandgap PBDTT‐FTTE:PC71BM to evaluate their transport characteristics. The standard cells for comparison are made of high‐quality poly(3,4‐ethylenedioxythiophene)/polystyrene‐sulfonate (PEDOT:PSS) hole transport layers (HTLs). Universal improvement is observed in the PCE by replacing the PEDOT:PSS with HVO (3.3–4.65% for P3HT:PC61BM; 5.34–7.12% for PBDTT‐FTTE:PC71BM). In the next step, the conventional ZnO electron transport layer (ETL) is replaced by an in‐house developed Nafion‐modified ZnO (NM‐ZnO) that shows a further efficiency boost of ≈39% (PCE 9.9%). Finally, the energy positioning of PBDTT‐FTTE:PC71BM is tuned by manipulating the molecular stacking through thermal treatment that leads to a champion efficiency 11.14%. IPSCs with HVO HTL show a superior shelf‐life over the course of 20 weeks.