Efficient and Stable Mesoscopic Perovskite Solar Cells Using a Dopant‐Free D–A Copolymer Hole‐Transporting Layer

Abstract

Addressing the stability issue in perovskite solar cells (PSCs) is a crucial step for commercialization purposes. Finding a novel and stable hole‐transporting layer (HTL) is one of the most effective strategies to solve this problem. Herein, a new polymeric HTL, namely poly{2,7‐[(5,5‐bis(3′,7′‐dimethyloctyl)‐5 H‐1,8‐dithia‐as‐indacenone]‐alt‐5,5‐[5′,6′‐bis(octyloxy)‐4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole]} (PDTIDTBT) is synthesized, indicating a great hole‐transporting property as compared with the commonly used 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) HTL. This polymer shows good mobility with suitable band alignment with respect to the triple A‐cation perovskite film, which is comparable with the state‐of‐art polymeric HTLs. Therefore, mesoscopic PSCs are fabricated by PDTIDTBT HTL and considered interface engineering technique using a thin layer of poly(methyl methacrylate) (PMMA) at the perovskite/HTL interface. Based on these modifications, a PSC with a maximum power conversion efficiency (PCE) of 19.89% is achieved, higher than the PCE of the spiro‐based PSC (19.28%). In addition, the PDTIDTBT‐based PSCs show excellent operational and ambient stability better than the spiro ones.

The versatility of polymers in perovskite solar cells

“…[107][108][109] By the SCLC approach, the hole mobilities of CH3O-PTAA, CH3-PTAA, and F-PTAA films were calculated to be 5.59 × 10 -5 , 4.38 × 10 -5, and 2.2 × 10 -5 cm 2 V -1 S -1 , respectively. 29,84 The hole mobility of PDTIDTBT was calculated to be 5.24× 10 -4 cm 2 V s -1 , as determined by the SCLC method, even higher than spiro-OMeTAD (8.1× 10 -5 cm 2 V s -1 ) 44 suggesting its suitability as a dopant-free HTM. 44,110 The high planar ladder-like conjugated backbone of IDTB, as well as S…O intramolecular interactions resulted in high hole mobility and passivation effect for perovskite.…”

“…29,84 The hole mobility of PDTIDTBT was calculated to be 5.24× 10 -4 cm 2 V s -1 , as determined by the SCLC method, even higher than spiro-OMeTAD (8.1× 10 -5 cm 2 V s -1 ) 44 suggesting its suitability as a dopant-free HTM. 44,110 The high planar ladder-like conjugated backbone of IDTB, as well as S…O intramolecular interactions resulted in high hole mobility and passivation effect for perovskite. The high hole mobility of undoped IDTB (2.89× 10 -5 cm 2 V s -1 ) was slightly lower than that of doped spiro-OMeTAD (5.97× 10 -5 cm 2 V s -1 ).…”

“…On the other hand, the Sonogashira cross-coupling reaction was applied for the preparation of PPY2 in presence of a palladium catalyst, a copper (I) cocatalyst, and an amine base as described in Scheme 6. PDTIDTBT 44,95 as a HTM for PSC was synthesized from Stille cross-coupling polycondensation from two monomers namely 2,7-dibromo-(5,5-bis(3´,5´dimethyloctyl)-5H-1,8-dithia-as-indacenone) (M1) and 5,5-bi(tributylstannyl)-(5´,6´dioctyloxy-4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole (M2) as outline in Scheme 8.…”

“…The measured Mn of 67.3 and 18.3 kDa with a polydispersity of 2.0 and 1.9, respectively. 9,44 The PDTPC and PPY2 exhibited the Mn of 11.4 and 7.7 kDa with a polydispersity of 1.69 and 1.90 by GPC, respectively. 45,46 10.4.…”

“…(B): IDTB copolymer and (C) RCP by Stille cross-coupling polycondensation, Reproduced from Ref. 9, Copyright 2020, Wiley-VCH 9,44,95.…”