Unraveling the Role of Energy Band Alignment and Mobile Ions on Interfacial Recombination in Perovskite Solar Cells

Abstract

A key limitation in perovskite solar cell (PSC) performance is suboptimal electronic properties at the perovskite–transport layer (TL) interfaces, which result in parasitic nonradiative recombination. Interface recombination depends on the concentration of recombination‐active defects, but as a recombination event requires both an electron and a hole, the magnitude and sign of charge accumulation at the perovskite–TL heterojunctions are also critical. Here, we employ a well‐established numerical ion‐electron drift‐diffusion model of PSCs to illustrate how the work function of the transport layer is an important factor in determining the total recombination activity at the perovskite interfaces. We show that the equilibrium electrostatics of the perovskite–TL heterojunctions, which are determined by the work function difference between the two materials, can result in increased recombination rates for any given concentration of interface defects. As a case study, we compare PSCs incorporating a NiOX hole transport layer with those with a spiro‐OMeTAD. We show that the work function of NiOX can induce greater electron accumulation at the perovskite–NiOX interface, which leads to increased interface recombination. Finally, a higher ion concentration is found to be beneficial to overall device performance by displacing accumulated electrons or holes at the TL interfaces and thus reducing recombination rates.

Performance limitations imposed by the TCO heterojunction in high efficiency perovskite solar cells

“…Several theoretical studies, including our own, have shown that altering the distribution of ionic charge, and concurrently the distribution of electrons and holes, can influence rates of non-radiative recombination, which ultimately explains many manifestations of hysteresis in PSCs. 13,15,20,21 In our theoretical exploration of the TCO's influence, we observed that the greater the influence of the TCO on the perovskite layer, the higher the rate of nonradiative recombination at any given defect density due to increased accumulation of minority charge carriers at the TL-TCO interface. This was consistent with our experimental observations in the substitution between TiO 2 and TiO x N y , 1 which showed an B8 mV increase in open circuit voltage.…”

Photoelectric Properties of Planar and Mesoporous Structured Perovskite Solar Cells

“…One of the most promising and environmentally friendly energy sources is electricity generated by solar cells. The organic-inorganic hybrid perovskite-based solar cells (PSC) show a promising future for photovoltaic technology [1]. During the last decade, the power conversion efficiency (PCE) of PSCs has grown from 3.8% to more than 25.7% [2], making them a very rapidly advancing technology and a popular topic in the field of solar cells.…”

“…During the last decade, the power conversion efficiency (PCE) of PSCs has grown from 3.8% to more than 25.7% [2], making them a very rapidly advancing technology and a popular topic in the field of solar cells. The high performance of PSCs can primarily be attributed to their excellent optoelectronic properties, such as (1) strong light absorption through the entire visible spectrum range, enabling the use of thin perovskite films [3,4]; (2) high carrier mobility [5,6]; (3) long carrier diffusion length [7,8]; (4) high defect tolerance [9]; and (5) long lifetime of the generated charge carriers [10,11]. To realize the good performance of a PSC, high-quality perovskite film containing a low density of defects must be employed in a single device [12].…”

“…To obtain perfectly operating perovskite devices, carrier transport and extraction layers are also important in addition to high-quality perovskite films [15,16]. There are several basic requirements for the transport layers: (1) good energy-level alignment with a perovskite for efficient charge transfer, (2) high mobility of charge carriers to guarantee their fast transport, (3) high transmittance to reduce the optical energy loss, (4) good stability, and (5) easy processing and low cost [16]. Two typical PSC structures are widely used: one is a planar heterojunction architecture [7,17], and another is a mesoporous structure [18,19].…”

Anchoring Grain Boundary via Aminated Carbon Nanotubes to Achieve Efficient and Stable Perovskite Solar Cells

“…Perovskite solar cells (PSCs) are emerging as the most promising optoelectronic devices due to the extraordinary optoelectronic properties of perovskite materials, such as tunable bandgap, high absorption coefficient and carrier mobility, high defect tolerance, and long-range carrier diffusion length. [1][2][3][4][5][6] After distinguished efforts have been devoted to the aspects of crystalline engineering, [7,8] interface engineering, [9,10] and additive strategy, [11,12] the record power conversation efficiency (PCE) of PSCs has been reached up to 25.8%. [13] To further improve the photovoltaic performance of single-junction PSCs beyond the Shockley-Quiesser limit of 33%, tandem solar cells based on transparent PSCs have gradually emerged and achieved major advancements.…”