Facile Approach for Efficient Non-Fullerene-Based Binary and Ternary Organic Solar Cells Using Hydrated Vanadium Pentoxide as a Hole Transport Layer

Abstract

Although the power conversion efficiency (PCE) of single-junction organic solar cells (OSCs) has exceeded more than 19%, the biggest obstacle to the commercial application of OSCs is the low device stability. Herein, this work reports the development of hydrated vanadium pentoxide (HVO) as a hole transport layer (HTL) with outstanding hole-extracting capabilities by a simple synthesis process and its use in the non-fullerene-acceptor-based binary and ternary OSCs. OSCs based on PM6:BTP-eC9 using an indium tin oxide/hydrated vanadium pentoxide (ITO/HVO) anode exhibit a maximum PCE of 13.33%, which is higher than ITO/poly(3,4-ethylene dioxythiophene):(polystyrene sulfonate) (PEDOT:PSS) (12.09%). Additionally, ternary (with an active layer of PM6:BTP-eC9:PC 71 BM) devices were also fabricated to analyze the impact of HVO HTL and achieved a PCE of 14.34%. The higher PCE is found to originate from the much higher work function (WF) of ITO/HVO than ITO/PEDOT:PSS. Furthermore, to replace a sophisticated thermal evaporation technique with a solution-processed, we fabricated inverted devices with HVO instead of control MoO 3 HTL. The highest occupied molecular orbital (HOMO) energy level of HVO is nearly equal to MoO 3 , and the device based on HVO attributed a PCE of 7.47%, which is higher than MoO 3 (6.70%)-based devices. This work provides a low-cost, highly efficient, and solution-processed HTL material for OSCs with long-term air stability.

Solution-Processed Co3O4-Based Hole Transport Layer for Nonfullerene Organic Solar Cells

“…Therefore, the HOMO level of Co 3 O 4 enables it to be suitable as an HTL compared to PEDOT:PSS and CATH when fabricating their devices. The high transmittance of the HTL prevents the photon absorption loss before reaching out to the active layer. , Based on TGA (dotted line in Figure a), the transmittance spectra of the Co 3 O 4 HTL at different temperatures (150, 250, and 350 °C) were recorded. As shown in Figure S5, lower transmittance was observed when increasing the TA temperature from 150 to 250 and 350 °C, which indicated a higher transmittance feature below 250 °C.…”

“…The high transmittance of the HTL prevents the photon absorption loss before reaching out to the active layer. 52,53 Based on TGA (dotted line in Figure 2a), the transmittance spectra of the HTL with UVO and TA at 150 °C attained an rms roughness value close to that of PEDOT:PSS. This results in a more uniform surface with a lower rms roughness, reducing the interfacial defects and enabling better interfacial contact of the active layer.…”

Vanadyl Sulfate Based Hole‐Transporting Layer Enables Efficient Organic Solar Cells

“…[ 60 ] Over past years, kinds of metal oxides with suitable WFs have been used to serve as HTL in OSCs, including vanadium oxide (V 2 O 5 ), molybdenum oxide (MoO 3 ), nickel oxide (NiO x ), and cobalt oxide (Co 3 O 4 ). [ 61‐66 ] These metal oxide type HTLs can be processed by either solution coating method or vacuum evaporation. Benefited from the good energy level alignment, high optical transmittance and high quality smooth films, OSCs using metal oxides as HTLs have achieved comparable high PCEs to those with PEDOT:PSS as HTL, and have been proven to be able to display improved stability.…”