Universal Bottom Contact Modification with Diverse 2D Spacers for High‐Performance Inverted Perovskite Solar Cells

Abstract

Although the 2D spacer modification is widely studied in perovskite solar cells (PVSCs), the energy level alignment between the 2D/3D interfaces makes it unfavorable for top surface passivation in the inverted p-i-n device structure. To address this issue, the effect of bottom interface modification is studied with three representative 2D spacers, i.e., the Ruddlesden-Popper 2D spacer, Dion-Jacobson 2D spacer, and strong passivation 2D spacer, in inverted p-i-n PVSCs. After optimization, the PVSCs with these 2D spacer modifications universally exhibit the best efficiencies of ≈21.6%, which constitutes dramatic improvement compared to the control device (20.7%). By lifting off the perovskite layer, the optoelectronic properties of the bottom surface are studied, and the mechanism underlying the improved device performance is unveiled to be uniformly originated from the formation of 2D/3D heterojunction, where the cascade valence band facilitates the hole collection and electron back scattering field suppresses the charge recombination at the anode interface. Besides, the unencapsulated device retains 90% of initial efficiency after 30 days of storage in ambient air with a relative humidity of 30 ± 5%, indicating excellent stability against moisture and oxygen. This study provides insight into the bottom interface modification with diverse 2D spacers for high-performance p-i-n structured PVSC devices.

Improvement in the Performance of Inverted 3D/2D Perovskite Solar Cells by Ambient Exposure

“…After PEAI surface modification, the average PCE decreased to %14.5% which was mainly due to a significant drop of J sc to %17.9 mA cm À2 , despite increased V oc and FF. This agrees with some of the literature reports, [19,45] and it can mainly be attributed to a decrease in short-circuit current density. [45] This decrease likely occurs due to insulating nature of PEAI [21] and/or worsening of the charge collection at the top interface with ETL.…”

“…[2][3][4][5][6][7][8][9][10][16][17][18][19][20][21][22][23][24]39,40,[44][45][46][47]49] Its use has been demonstrated to improve stability of MA-based, [3] formamidinium (FA)based, [2,4,7] and Cs-based perovskites, [40] as well as mixed composition perovskites. [4,5,[8][9][10] In addition, it has been used as an additive to the perovskite to produce varying amounts and different 2D/quasi-2D phases, [7,16,18,23,40] and to modify perovskite interfaces with electrode, [9] top hole transport layer (HTL), [5,6,8,10,44] bottom HTL, [20,39,45,49] top electron transport layer (E...…”

“…[19,49] Thus, it has been used both in inverted [20][21][22]29,39,45,49] and conventional [5,6,8,10,44] architecture devices, but its use in inverted devices has been somewhat controversial because contradictory results (worsening and improvement of the efficiency) have been reported in the literature when the phenylethylammonium iodide (PEAI) is applied to the top interface of the perovskite. [20][21][22]29,45,49] The 2D perovskite layer on the surface of the 3D layer is typically formed by surface treatment. [4] Surface treatment with PEAI in isopropanol (IPA) solution has been shown to lead to 2D perovskite formation due to the dissolution of MA þ or FA þ from the perovskite surface, facilitated by highly polar nature of IPA.…”

A dopant-free hole transport material boosting the performance of inverted methylamine-free perovskite solar cells

“…For example, these materials are dopant-free HTMs, which are beneficial to reduce the hysteresis and improve the stability of devices. 8–10…”

Reduction of Nonradiative Loss in Inverted Perovskite Solar Cells by Donor−π–Acceptor Dipoles

“…In order to improve the efficiency of IPSCs, a lot of efforts have been done. For example, additives including polymers, ionic liquids, and small molecules were applied to manipulate the perovskite crystallization to obtain high-quality perovskite films with low trap density. − In addition, new charge transport materials such as phenoxazine-based materials and carbazole-based molecules have been developed to enhance the charge collection. − Besides, interface engineering is also a critical method to improve the performance of the IPSCs. − Currently, the certified results of over 22% were obtained. However, the nonradiative loss in IPSCs is still larger than that in the regular device, leading to a lower open-circuit voltage ( V oc ) and fill factor (FF), which may originate from the insufficient defect passivation and inefficient charge collection. ,, Commonly used passivating agents in IPSCs include fullerene derivatives, wide band gap materials, and insulating polymers such as poly­(methyl methacrylate) and polystyrene. − However, the fullerene derivatives can only function as chemical passivators and may introduce energy disorder, while the wide band gap materials and insulating polymers may hinder the charge extraction. , Recently, surface dipoles that are capable of simultaneously passivating the defects and reinforcing the built-in electric field to facilitate the charge collection and therefore reduce the nonradiative loss have been reported. − However, a comprehensive investigation is still missing to disclose the relationship between the electronic structures of dipole molecules and the reinforcement of the built-in electric field.…”