A Universal Double‐Side Passivation for High Open‐Circuit Voltage in Perovskite Solar Cells: Role of Carbonyl Groups in Poly(methyl methacrylate)

Although perovskite solar cells (PVSCs) have achieved rapid progress in the past few years, most of the high‐performance device results are based on the doped small molecule hole‐transporting material (HTM), spiro‐OMeTAD, which affects their long‐term stability. In addition, some defects from under‐coordinated Pb atoms on the surface of perovskite films can also result in nonradiative recombination to affect device performance. To alleviate these problems, a dopant‐free HTM based on a donor‐acceptor polymer, PBT1‐C, synthesized from the copolymerization between the benzodithiophene and 1,3‐bis(4‐(2‐ethylhexyl)thiophen‐2‐yl)‐5,7‐bis(2‐alkyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione units is introduced. PBT1‐C not only possesses excellent hole mobility, but is also able to passivate the surface traps of the perovskite films. The derived PVSC shows a high power conversion efficiency of 19.06% with a very high fill factor of 81.22%, which is the highest reported for dopant‐free polymeric HTMs. The results from photoluminescence and trap density of states measurements validate that PBT1‐C can effectively passivate both surface and grain boundary traps of the perovskite.

mentioning

confidence: 99%

A Dopant‐Free Polymeric Hole‐Transporting Material Enabled High Fill Factor Over 81% for Highly Efficient Perovskite Solar Cells

Feng

Deng

et al. 2019

“…As the passivation of perovskite/ETL and perovskite/HTL are beneficial to reduce defects at the surfaces, it is easy to consider to minimize defects at both interfaces. For example, the passivated PSCs inserting an ultrathin PMMA films at both the perovskite/spiro‐MeOTAD and perovskite/TiO 2 interfaces boosted the V oc from 1.17 eV (passivated PSCs only at perovskite/TiO 2 interface) to 1.21 V . PbI 2 was also applied as passivation layer and a double‐side‐passivated PSCs by distributing PbI 2 to both front/rear‐side surfaces yielded PCE of 22.3%, which was better than the device with only passivation in the perovskite/spiro‐MeOTAD interface of PCE 21.6% and without passivation of 18.8% .…”

Section: Defects and Interface Engineeringmentioning

confidence: 99%

Progress of Surface Science Studies on ABX₃‐Based Metal Halide Perovskite Solar Cells

Qiu

Ono

et al. 2019

107

ABX3 type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing toward their theoretical limit. To gain the full potential of PSCs relies on the understanding of the device working mechanisms and recombination, the material quality, and the match of energy levels in the device stacks. In this review, the importance of designing PSCs from the viewpoint of surface/interface science studies is presented. For this purpose, recent case studies are discussed to demonstrate how probing of local heterogeneities (e.g., grains, grain boundaries, atomic structure, etc.) in perovskites by surface science techniques can help correlate material properties and PSC device performance. At the solar cell device level with active areas larger than millimeter scale, the ensemble average measurement techniques can characterize the overall average properties of perovskite films as well as their adjacent layers and provide clues to understand better the solar cell parameters. How generation and healing of electronic defects in perovskite films limit the device efficiency, reproducibility, and stability, and induce the time‐dependent transient behavior in the current‐voltage curves are also the central focus of this review. On the basis of these studies, strategies to further improve efficiency and stability, as well as reducing hysteresis are presented.

“…[59] Therefore, PMMA might be considered as the polymeric spacer model to avoid detrimental interaction at the PSC interfaces. We explored different materials, relying on the noncapacitive hysteresis as a figure of merit.…”

Section: Resultsmentioning

confidence: 99%

Stability and Dark Hysteresis Correlate in NiO‐Based Perovskite Solar Cells

Girolamo

Matteocci

Kosasih

et al. 2019

for commercialization. [2,3] Thus, if metal halide perovskite (PSK) solar cells are to take part in supplying the world's energy demand, device stability must be significantly improved.Several kinds of stimuli have been found to degrade PSCs. When exposed to moist atmosphere, CH 3 NH 3 PbI 3 (MAPI) undergoes an irreversible degradation via the formation of hydrated phases. [4,5] Even the all-inorganic perovskite CsPbBr 3 undergoes intricate structural modifications when exposed to relative humidity (RH) above 60%, highlighting the sensitivity of lead halide perovskites to moisture also in the absence of organic cations. [6] Perovskites are also sensitive to atmospheric oxygen, which can rapidly diffuse inside the perovskite film through grain boundaries and inside the lattice via iodine vacancies. [7] Under illumination, the superoxide anion (O 2 − ) forms, which is highly reactive and triggers lattice decomposition. [8,9] Nevertheless, proper encapsulation procedures [10,11] can mitigate or, in the best scenario, eliminate the influence of moisture or oxygen on device stability. In addition to that, metal halide perovskites are also sensitive to heat, illumination, and electrical bias, three certain conditions in photovoltaic operation. In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite's halides has been reported for both molecular and polymeric hole selective layers (HSLs), and here it is shown that also NiO brings about this decomposition mechanism.Employing NiO as an HSL in p-i-n PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is attributable to the bias-induced degradation of perovskite/NiO interface. The possibility of electrochemically decoupling NiO from the perovskite via the introduction of a buffer layer is explored. Employing a hybrid magnesiumorganic interlayer, the noncapacitive hysteresis is entirely suppressed and the device's electrical stability is improved. At the same time, the PCE is improved up to 18% thanks to reduced interfacial charge recombination, which enables more efficient hole collection resulting in higher V oc and FF.