Analyzing Interface Recombination in Lead‐Halide Perovskite Solar Cells with Organic and Inorganic Hole‐Transport Layers

Abstract

The interfaces between absorber and transport layers are shown to be critical for perovskite device performance. However, quantitative characterization of interface recombination has so far proven to be highly challenging in working perovskite solar cells. Here, methylammonium lead halide (CH3NH3PbI3) perovskite solar cells are studied based on a range of different hole‐transport layers, namely, an inorganic hole‐transport layer CuOx, an organic hole‐transport layer poly(triarylamine) (PTAA), and a bilayer of CuOx/PTAA. The cells are completed by a [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/bathocuproine/Ag electron contact. Energy levels are characterized using photoelectron spectroscopy and recombination dynamics by combining steady‐state photoluminescence and transient photoluminescence with numerical simulations. While the PTAA‐based devices hardly show any interface recombination losses and open‐circuit voltages >1.2 V, substantial losses are observed for the samples with a direct CuOx/perovskite interface. These losses are assigned to a combination of energetic misalignment at the CuOx/perovskite interface coupled with increased interface recombination velocities at the perovskite/PCBM interface.

Interface Optimization via Fullerene Blends Enables Open‐Circuit Voltages of 1.35 V in CH3NH3Pb(I0.8Br0.2)3 Solar Cells

“…In the latter case, the assumed bulk lifetime must be unphysical and a longer lifetime has to be assumed. The values of the surface‐recombination velocity presented here are slightly higher than what was previously estimated for the PTAA/MAPI interface [ 4 ] based on Tr‐PL measurements but slightly lower than previous estimates [ 76,79 ] for recombination at the MAPI/PCBM interface. The surface‐recombination velocity of PCBM in the assumed bulk lifetime range is nearly one order of magnitude higher than S for CMC:ICBA.…”

“…Interface recombination is affected both by the energy‐level alignment [ 73–75 ] at the interface between absorber and both charge transport layers and by its kinetics that are typically expressed in terms of surface‐ or interface‐recombination velocities. [ 76 ] Here, we will first study the kinetics of recombination using transient photoluminescence measurements and subsequently the energy‐level alignment of the different fullerenes by a combination of ultraviolet photoelectron spectroscopy (UPS) and photothermal deflection spectroscopy (PDS).…”

“…In addition to surface quality the energy alignment between perovskite and CTL limits the V oc . [ 12,76 ] Large offsets, e.g., in the conduction band at the absorber–ETL interface would lead to an interfacial bandgap at this interface that is substantially lower than the bulk bandgap. If recombination is efficient via the interface (i.e., electrons in the ETL can efficiently recombine with holes in the perovskite), the interface may strongly deteriorate the V oc .…”

Impact of Photoluminescence Reabsorption in Metal‐Halide Perovskite Solar Cells

“…More details can be found in our previous work. [ 19 ] As qV oc is typically smaller than μ PVK caused by the limited charge selectivity of contacts, charge recombination at the contacts, and the energetic offset of majority carriers at the interfaces, [ 20,46–53 ] Figure 3d,e cannot confirm that PLr reduces μ PVK in our FAMACs PSCs. However, Figure 3e shows that neglecting PLr results in an overestimation of the effective k nr .…”

“…More details can be found in our previous work. 19 Since qVoc is typically smaller than µPVK caused by the limited charge selectivity of contacts, charge recombination at the contacts, and the energetic offset of majority carriers at the interfaces, 20,[46][47][48][49][50][51][52][53]…”