Interface-Dependent Radiative and Nonradiative Recombination in Perovskite Solar Cells

Abstract

Interfacial engineering has shown to play an essential role to optimize recombination losses in perovskite solar cells; however, an in-depth understanding of the various loss mechanisms is still underway. Herein, we study the charge transfer process and reveal the primary recombination mechanism at inorganic electron-transporting contacts such as TiO2 and its modified organic rivals. The modifiers are chemically ([6,6]-phenyl C61 butyric acid, PC60BA) or physically ([6,6]-phenyl C61 butyric acid methyl ester, PC60BM and C60) attached fullerene to the TiO2 surface to passivate the density of surface states. We do not observe any change in morphology, crystallinity, and bulk defect density of halide perovskite (CH3NH3PbI3 in this case) upon interface modification. However, we observe compelling results via photoluminescence and electroluminescence studies that the recombination dynamics at both time scales (slow and fast) are largely influenced by the choice of the selective contact. We note a strong correlation between the hysteresis and the so-called slow charge dynamics, both significantly influenced by the characteristics of the selective contact, for example, the presence of surface traps at the selective contact not only shows a larger hysteresis but also leads to higher charge accumulation at the interface and distinguishable slow dynamics (a slower stabilization of recombination dynamics at a time scale of several minutes).

A Cryogenic Process for Antisolvent‐Free High‐Performance Perovskite Solar Cells

“…The residual hysteresis in our devices after optimization of perovskite quality is attributed to the surface traps, which is also consistent with slow increase of photocurrent observed in current–time ( I – t ) scan shown in Figure S9 of the Supporting Information . It was also reported that the hysteresis is related to the energy level alignment at ETL/perovskite interface, which in turn is affected by the presence of deep trap states .…”

“…In addition to the reduction in the interface trap density, improvements in the conductivity of SnO 2 may also contribute to reduced hysteresis . Since the observed behaviors (hysteresis and slow stabilization dynamics) are consistent with the presence of interface traps rather than bulk traps in the perovskite layer, it is possible that the performance could be further improved by optimizing ETL deposition as well as the optimization of the interface between the ETL and the perovskite layer—an effect analogous to PSCs with mesoscopic ETL typically demonstrate smaller I – V hysteresis …”

“…Meanwhile light soaking effect is observed for c‐SnO 2 based devices but not for c‐SnO 2 /SnO 2 ‐NPs based devices. It is speculated that the trap filling action at c‐SnO 2 interface is accounted for the observed behaviors and their effects can be alleviated by optimizing the c‐SnO 2 /perovskite interface with SnO 2 ‐NPs. The correlation between the defect density and the quality of SnO 2 ETL will be systematically investigated in the coming works.…”

Charge extraction via graded doping of hole transport layers gives highly luminescent and stable metal halide perovskite devices

“…An effective way to remove these defects apart from a chemical modification of perovskite ( 4 ) is to introduce passivation treatments and interlayers between the perovskite and the electron transport layer (ETL)/hole transport layer (HTL) ( 5 , 6 ). It has been intensively shown that treating mesoporous TiO 2 , arguably the most common ETL in PSCs, reduces electron trap state density and enables faster electron transport ( 7 – 9 ). The interface between perovskite and the HTL [e.g., doped 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenyl-amine)9,9′-spirobifluorene, denoted as Spiro-OMETAD] is equally crucial, and to obtain maximum PCE, this needs to be enhanced simultaneously (e.g., to achieve faster hole transport).…”

A Modulated Double‐Passivation Strategy Toward Highly Efficient Perovskite Solar Cells with Efficiency Over 21%

“…It is reported that nonradiative trap-assisted recombination plays a very important function in the FF of PSCs. [16][17][18] Also, it should deserve special notice that compared with other photovoltaic materials in solar cells such as silicon, polycrystalline perovskite includes under-coordinated ions as defects at the surface and grain boundaries of their crystal, which are considered as the centers of Shockley-Read-Hall nonradiative recombination. [19] These unique defects on the surface and grain boundary can lead to severe carrier recombination in the polycrystalline perovskite thin film.…”