Organic–inorganic hybrid perovskite solar cells (PSCs) have made unprecedented progress in the past ten years, the power conversion efficiency of which increased from 3.8% in 2009 to 25.5% in 2020. The choice of hole transport layers (HTLs) is a key factor for achieving efficient and stable PSCs. Recently, 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) has been proven to be the most suitable small molecule HTL material in n–i–p PSCs. However, the conductivity and hole mobility of spiro-OMeTAD are dependent on the dopants. Bis(trifluoromethane)sulfonamide lithium salt (LiTFSI) and 4-tert-butylpyridine (TBP) have become the standard HTL dopants to improve the charge transport properties of n–i–p PSCs. Both of these two dopants are effective but have a negative impact on the device stability (induced by ion migration, hygroscopicity, and corrosiveness). In response, lots of efforts have been devoted to the development of alternative and new dopants. In this review, the influence of different doping strategies and corresponding doping mechanisms on device performance and stability was mainly discussed. The stability issues of doped spiro-OMeTAD based PSCs were also described. Finally, we proposed some possible future research goals for dopants based on these existing results to obtain long-lasting and high-efficiency PSCs.

Strategies of modifying spiro-OMeTAD materials for perovskite solar cells: a review

Wide Bandgap Polymer with Narrow Photon Harvesting in Visible Light Range Enables Efficient Semitransparent Organic Photovoltaics

Applications of Self-Assembled Monolayers for Perovskite Solar Cells Interface Engineering to Address Efficiency and Stability

Passivation of defects in perovskite solar cell: From a chemistry point of view

Barrier Designs in Perovskite Solar Cells for Long-Term Stability

Organic–inorganic hybrid perovskite solar cells (PSCs) has achieved the power conversion efficiency (PCE) of 25.2% in the last 10 years, and the PCE of inverted PSCs has reached >22%. The rapid enh...

Recent Progress of Inverted Perovskite Solar Cells with a Modified PEDOT:PSS Hole Transport Layer.

Improving the performance of perovskite solar cells by surface passivation

Carbon dots (CDs) have significant potential in the chemical decoration, crystal modification, and surface passivation of perovskite photovoltaics. However, incompatibility between the hydrophilic/hygroscopic nature of CDs and moisture sensitive perovskite remains an issue. Solving this problem would yield a significant improvement for stable perovskite devices embedded with CDs. Herein, hydrophobic passivation layers are realized for perovskite solar cells (PSCs) through the surface engineering of CDs, exploiting electrostatic self-assembly of trichloro(3,3,3-trifluoropropyl)silane (C3H4Cl3F3Si) and CDs. The embedded CDs modify perovskite grains and passivate grain boundary defects, thereby promoting the carrier lifetime and charge collection. The inserted C3H4Cl3F3Si insulating layer provides a tunneling junction at the contact of the perovskite and electron transport layer. This tunneling layer can selectively conduct electrons and block holes, which spatially separate photo-generated carriers to suppress their recombination. As a result, the optimized perovskite devices deliver the highest efficiency of 21.12% with a high fill factor of 82.86%. Moreover, the variation of surface wettability can be achieved by the self-assembly of C3H4Cl3F3Si, which improves the stability of perovskite devices by maintaining nearly 90% efficiency for over 30 days' exposure to an ambient atmosphere without encapsulation.

Incorporating self-assembled silane-crosslinked carbon dots into perovskite solar cells to improve efficiency and stability

To overcome the zigzag pathway transport of the electron diffusion process and eliminate the surface trap states of phenyl-C61-butyric acid methyl ester (PCBM) nanofilms in inverted perovskite solar cells, novel 1D N-type doped carbon nanorods (CNRs) are developed by a stibonium (Sb) auxiliary ball milling method and introduced into the PCBM film to prepare the PCBM:Sb-CNRs hybrid transport layer. In this way, the N-type doped Sb-CNRs can extend the built-in electric field between CH3 NH3 PbI3 and PCBM to facilitate the separation of electron/hole pairs. The discontinuous band with the built-in potential in the PCBM/Sb-CNRs heterojunction can boost interfacial charge redistribution and promote electrons diffusion from PCBM to electrode through 1D Sb-CNRs network. As a result, the high device efficiency of 19.26% with enhanced air stability and little hysteresis are achieved. This work demonstrates a simple strategy to improve the efficiency and stability of perovskite photovoltaic devices using low-cost carbon nanomaterials.

Guanhua Ren

Papers

Strategies of modifying spiro-OMeTAD materials for perovskite solar cells: a review

Recent Progress of Inverted Perovskite Solar Cells with a Modified PEDOT:PSS Hole Transport Layer.

Improving the performance of perovskite solar cells by surface passivation

Incorporating self-assembled silane-crosslinked carbon dots into perovskite solar cells to improve efficiency and stability

Developing 1D Sb-Embedded Carbon Nanorods to Improve Efficiency and Stability of Inverted Planar Perovskite Solar Cells.