Nonradiative Recombination in Perovskite Solar Cells: The Role of Interfaces

Abstract

Perovskite solar cells combine high carrier mobilities with long carrier lifetimes and high radiative efficiencies. Despite this, full devices suffer from significant nonradiative recombination losses, limiting their VOC to values well below the Shockley–Queisser limit. Here, recent advances in understanding nonradiative recombination in perovskite solar cells from picoseconds to steady state are presented, with an emphasis on the interfaces between the perovskite absorber and the charge transport layers. Quantification of the quasi‐Fermi level splitting in perovskite films with and without attached transport layers allows to identify the origin of nonradiative recombination, and to explain the VOC of operational devices. These measurements prove that in state‐of‐the‐art solar cells, nonradiative recombination at the interfaces between the perovskite and the transport layers is more important than processes in the bulk or at grain boundaries. Optical pump‐probe techniques give complementary access to the interfacial recombination pathways and provide quantitative information on transfer rates and recombination velocities. Promising optimization strategies are also highlighted, in particular in view of the role of energy level alignment and the importance of surface passivation. Recent record perovskite solar cells with low nonradiative losses are presented where interfacial recombination is effectively overcome—paving the way to the thermodynamic efficiency limit.

Relation between Fluorescence Quantum Yield and Open‐Circuit Voltage in Complete Perovskite Solar Cells

“…[34,35] If accumulated in a too large amount at the electron transport layer/perovskite interface, it introduces simultaneously a negative energy mismatch with SnO 2 and a positive mismatch with the perovskite, as shown in the proposed energy diagram of Figure 5c. [41] Such opposite mismatches are responsible for an internal voltage drop due to the offset of the electron quasi-Fermi level [19,[47][48][49] and a degraded electron extraction, [50,51] respectively. Similar effects can be caused due to a too-large PbI 2 excess at the perovskite/Spiro-OMeTAD interface.…”

“…In fact, it is only very recently that works discussing the correlation between QY and V oc of PSCs on the basis of experimental results have emerged. [15,16,18,19] In the most recent works, [9,18] the QY and V oc of PSCs with different transport layers were compared. Differences between V oc and QFLS were observed, and their origin was discussed in relation to energy-level offsets at interfaces.…”

“…Differences between V oc and QFLS were observed, and their origin was discussed in relation to energy-level offsets at interfaces. A very recent review of advances on this matter is provided by Wolff et al [19] Herein, measurements of the QY and photovoltaic properties of a series of complete solar cells based on a FA 0.8 MA 0.2 PbI 3Ày Br y perovskite produced by the two-step method are reported (Section 2.1). By combining these measurements with electromagnetic calculations, the dominant nonidealities in the studied devices are discussed.…”

Multifunctional Phosphorus‐Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture‐Stable Perovskite Solar Cells

“…First, surface defects play the role of recombination center. [ 10 ] The poor charge extraction induced by the imperfect perovskite/transporting layer interfaces results in the low short‐circuit current ( J SC ) and fill factor (FF). These surface defects also lead to band bending and Fermi energy pinning, limiting the open‐circuit voltage ( V OC ).…”

High voltage vacuum-processed perovskite solar cells with organic semiconducting interlayers

“…6 Several studies have been focused on the understanding of charge transfer and interfacial processes between the perovskite, the ETLs, and the electrode, with the ultimate goal of maintaining a high charge collection efficiency and to abate non-radiative charge recombination. 7 Among ETLs, notable examples are n-type metal oxides, 8 in particular TiO 2 and SnO 2 , while the most widely adopted organic semiconductors are fullerene derivatives. 9 Fullerenes cannot only selectively transport electrons between the perovskite and the electrode, but are also capable to effectively passivate trap states and mitigate ionic migration at the perovskite surface and at the grain boundaries.…”