Molecular engineering of conjugated polymers for efficient hole transport and defect passivation in perovskite solar cells

Abstract

Organic-inorganic hybrid perovskite solar cells represent an exceptional candidate for nextgeneration photovoltaic technology. However, the presence of surface defects in perovskite crystals limits the performance as well as the stability of perovskite solar cells. We have employed a series of carbazole and benzothiadiazole (BT) based donor-acceptor copolymers, which have different lengths of alkoxy side-chains grafted on the BT unit, as the dopant-free hole transport materials (HTMs) for perovskite solar cells. We demonstrate that although these side-chains can reduce the  stacking structural order of these copolymers to affect the hole transport properties, the methoxy unit introduces a desired defect passivation effect. Compared to the Spiro-OMeTAD-based device, the copolymer with methoxy side-chains on the BT unit (namely PCDTBT1) as the HTM achieved superior power conversion efficiency and stability due to efficient hole transport and the suppression of trap-induced degradation, whilst the copolymer with octyloxy side-chains on the BT unit (namely PCDTBT8) as the HTM lead to poor performance and stability.

Management of Crystallization Kinetics for Efficient and Stable Low‐Dimensional Ruddlesden–Popper (LDRP) Lead‐Free Perovskite Solar Cells

“…The high V oc and J sc observed in "L-I" based device are mainly due to the high quality films and ultralarge grain size. Moreover, as shown in Figure S8 (Supporting Information), the V oc versus light intensity characterization also confirm that the reduced charge recombination [38] and the lowered trap density of the "L-I" device (n = 0.094) compared to those of DMSO (n = 0.153) and MAAc (n = 0.101) devices, resulting in the effective transfer and extraction of charge. As shown in Figure 4b, the device fabricated from "L-I" process showed the lowest background carrier concentration, which, on one hand, indicated the lower p-doping level and lower trap state density attributed to the inhibition of oxidation of Sn 2+ compared to that of devices from DMSO and MAAc processes, corresponding to the results of XPS (Figure 2d-f) and SCLC (Figure 3); on the other hand, demonstrated the significantly reduced charge recombination.…”

Core Structure Engineering in Hole‐Transport Materials to Achieve Highly Efficient Perovskite Solar Cells

“…It works to extract and transfer holes and prevents the perovskite layer from directly contacting the electrode . Moreover, the charge‐transport layers play an extremely important role in suppressing charge recombination, which may bring about a high open‐circuit voltage ( V oc ) and PCE . Therefore, developing efficient hole‐transport materials (HTMs) is an effective and useful method to obtain highly efficient PSCs.…”

High‐Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency

“…Furthermore,w eu tilized the relationships between photoelectric response and imported light intensity to estimate the recombination reactions within devices.B yp lotting J sc and V oc as afunction of incident light intensity (I), as shown in Figure 3c,d, the recombination mechanism can be understood according to the following equations [Eqs. (4) and (5)]: [24,25] J sc / I a ða 1Þð 4Þ…”