Stable perovskite solar cells with efficiency of 22.6% via quinoxaline-based polymeric hole transport material

Abstract

Poor stability of spiro-OMeTAD hole transport materials (HTMs) with dopant is a major obstacle for the commercialization of perovskite solar cells (pero-SCs). Herein, we demonstrate a series of quinoxaline-based D-A copolymers PBQ5, PBQ6 and PBQ10 as the dopant-free polymer HTMs for high performance pero-SCs. The D-A copolymers are composed of fluorothienyl benzodithiophene (BDTT) as D-unit, difluoroquinoxaline (DFQ) with different side chains as A-unit, and thiophene as π-bridge, where the side chains on the DFQ unit are bi-alkyl for PBQ5, bi-alkyl-fluorothienyl for PBQ6, and alkoxyl for PBQ10. All the three copolymers are adopted as the dopant-free HTM in the pero-SCs. The planar n-i-p structured pero-SCs based on (FAPbI 3 ) 0.98 (MAPbBr 3 ) 0.02 with PBQ6 HTM demonstrated the high power conversion efficiency (PCE) of 22.6% with V oc of 1.13 V and FF of 80.8%, which is benefitted from the suitable energy level and high hole mobility of PBQ6. The PCE of 22.6% is the highest efficiency reported in the n-i-p structured pero-SCs based on dopant-free D-A copolymer HTM. In addition, the pero-SCs show significantly enhanced ambient, thermal and light-soaking stability compared with the devices with traditional spiro-OMeTAD HTM.

Quinoxaline‐Based D–A Copolymers for the Applications as Polymer Donor and Hole Transport Material in Polymer/Perovskite Solar Cells

“…[92] Very recently, Lu et al employed three abovementioned highly efficient Qx-based D-A copolymers PBQ5, PBQ6, and PBQ10 (see Figure 2) as the single dopant-free HTM in the planar n-i-p structured pero-SCs in considering their appropriate electronic energy levels and high hole mobilities. [94] The three copolymers show low-lying HOMO energy levels, and PBQ6 has the lowest HOMO energy level and the best alignment with perovskite photoactive layer based on (FAP bI 3 ) 0.98 (MAPbBr 3 ) 0.02 . Importantly, PBQ6 possesses relatively better film thickness tolerance up to 90 nm due to its higher hole mobility.…”

“…Therefore, employing high-quality HTM is critical to reduce the defects and suppress the charge recombination at the electrode interface of the pero-SCs. [92][93][94] To address these issues, the Qx-based D-A copolymers are used as HTM for highly efficient and stable pero-SCs recently. [92,94] In 2018, Meng et al employed the above-mentioned lowcost and stable D-A copolymer PTQ10 as interfacial layer for the planar n-i-p structured pero-SCs (Figure 6).…”

“…[92][93][94] To address these issues, the Qx-based D-A copolymers are used as HTM for highly efficient and stable pero-SCs recently. [92,94] In 2018, Meng et al employed the above-mentioned lowcost and stable D-A copolymer PTQ10 as interfacial layer for the planar n-i-p structured pero-SCs (Figure 6). [92] First, the polymer PTQ10 offers a deep HOMO energy level to form a good energy level alignment with the valence band of the perovskite, which facilitates the hole extraction.…”

“…In addition, due to the good film forming property and film thickness tolerance, PBQ6 exhibits outstanding processability with blade coating technique, and the large-area devices of 1 cm 2 with blade-coated PBQ6 hole transport layer also achieved high PCE of 21.1%. [94] Moreover, due to the intrinsically better stability and dopant-free characteristic of the polymer HTM, the devices with polymer PBQ6 as HTM show significantly enhanced ambient, thermal, and light-soaking stability, [94] making PBQ6 a promising HTM for potential commercialization of the pero-SCs.…”

Recent advances in dopant-free organic hole-transporting materials for efficient, stable and low-cost perovskite solar cells

“…In 2021, Li and Meng et al constructed a series of D–A copolymers based on fluorothienyl benzodithiophene (BDTT) and difluoroquinoxaline (DFQ) segments as D and A units, respectively, namely, PBQ5, PBQ6 and PBQ10. 133 By introducing alkylfluorothienyl as a side chain of the DFQ segment, the resultant polymer PBQ6 offered the lowest HOMO energy (−5.43 eV) and the best match with the perovskite layer, and the highest hole mobility (4.6 × 10 −4 cm 2 V −1 s −1 ) attributed to the best planar structure and the highest degree of crystallinity, leading to an effective charge carrier extraction and transport at the interface. Owing to the faster charge transfer and lowest trap-assisted recombination loss, PBQ6 as a dopant-free HTM in planar PSC based on MAFAPbI x Br 3− x achieved a superior PCE up to 22.6% with a very high V oc of 1.13 V and an FF of 80.8%, which is a top-ranking PCE in the n–i–p PSCs based on a dopant-free D–A copolymer HTM.…”