Donor–Acceptor Type Polymer Bearing Carbazole Side Chain for Efficient Dopant‐Free Perovskite Solar Cells

Abstract

In conventional n–i–p perovskite solar cells (PVSCs), electron donor (D)–acceptor (A) polymers have been found to be potential substitutes for doped spiro‐based small molecule hole‐transporting materials (HTMs) due to their excellent performance in hole mobility, film formability, and stability. Herein, a benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐benzodithiophene‐4,8‐dione (BDD) copolymer PBDB‐Cz is developed by employing carbazole as the conjugated side chain of BDT. PBDB‐O and PBDB‐T with alkoxy and thiophene as the side chain of BDT, respectively, are also synthesized and studied for comparison. The synergistic effect of the carbazole side chain and the BDT‐BDD backbone to promote hole transport properties is found in PBDB‐Cz. The carbazole side chain enhances both coplanarity and interaction of polymer chains, while simultaneously deepening energy levels and improving the hole mobility of the polymeric HTM. Consequently, PBDB‐Cz outperforms two counterparts, exhibiting a promising power conversion efficiency (PCE) of 22.06%. Notably, the PBDB‐Cz also improves the device stability, and the devices can retain more than 90% of their initial PCEs after being stored at ambient conditions for 100 days. To the best of the authors’ knowledge, this is the first report to incorporate carbazole into D–A polymeric HTM by side chain engineering.

Collaborative Strategy of Multifunctional Groups in Trifluoroacetamide Achieving Efficient and Stable Perovskite Solar Cells

“…Figure 4d presents the J – V curves of the PSCs without and with TFAA additive in both the reverse and forward scan, and the corresponding hysteresis index (HI = (PCE reverse − PCE forward )/PCE reverse ) are listed in Table S3, Supporting Information. [ 47,48 ] The calculated HI remarkably reduces from 14.12% for the control device to 2.32% for the TFAA‐modified cell, suggesting that the incorporation of the TFAA greatly passivates the defect density in the perovskite and facilitates the charge extraction from the perovskite/Spiro‐OMeTAD interface. To explore the reproducibility of device performance, the statistical distribution of photovoltaic parameters of 40 cells is depicted (Figure S7, Supporting Information) and the average photovoltaic parameters with standard deviation are tabulated (Table S4, Supporting Information).…”

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

“…Recently, they adopted BDT derivative units in place of the IDT unit to construct a series of D–A copolymers, namely, PBDB-O, PBDB-T and PBDB-Cz. 139 Compared with the alkoxy-substituted PBDB-O and alkylthiophene-substituted PBDB-O, the carbazoly-substituted PBDB-Cz increased both the coplanarity and interaction of polymer chains, leading to the highest hole mobility. Finally, an outstanding PCE of 22.0% has been achieved in the dopant-free PBDB-Cz-based PSC, while the PBDB-O and PBDB-T-based devices only showed PCEs of 10.2% and 19.0%, respectively.…”

Configurable Organic Charge Carriers toward Stable Perovskite Photovoltaics

“…A majority of the studies have thus been focused on the design and selection of appropriate electron-withdrawing and donating units. ,,− ,,− The ideal pairs of donor and acceptor should allow more maximized built-in potential, resulting in an enhanced electric field for photogenerated exciton separation and charge extraction . Thus far, several high-performing donor–acceptor pairs have been incorporated to yield efficiencies of around 20%. ,,,,,, These include benzo­[1,2- b :4,5- b ′]­dithiophene (BDT), which stands out as the most prevalent electron-donating moieties owing to its high coplanarity that facilitates charge transport. BDT is often coupled with the acceptor unit benzo­thiadiazole (BT). − Some other common donor–acceptor pairs include the electron rich phenoxazine or phenylaniline units paired with the electron-deficient imidazole derivatives .…”