Recent progress in perovskite solar cells:material science

Perovskite solar cells represent a promising third-generation photovoltaic technology with low fabrication cost and high power conversion efficiency.In light of the rapid development of perovskite materials and devices,a systematic survey on the latest advancements covering a broad range of related work is urgently needed.This review summarizes the recent major advances in the research of perovskite solar cells from a material science perspective.The discussed topics include the devices based on different type of perovskites(organic-inorganic hybrid,all-inorganic,and lead-free perovskite and perovskite quantum dots),the properties of perovskite defects,different type of charge transport materials(organic,polymeric,and inorganic hole transport materials and inorganic and organic electron transport materials),counter electrodes,and interfacial materials used to improve the efficiency and stability of devices.Most discussions focus on the key progresses reported within the recent five years.Meanwhile,the major issues limiting the production of perovskite solar cells and the prospects for the future development of related materials are discussed.

In-situ growth of low-dimensional perovskite-based insular nanocrystals for highly efficient light emitting diodes

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices.However,judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology,composition,and defect.Herein,we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization.The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX_(3) perovskite,respectively.The formation of supramolecular structure retard perovskite nucleation,while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth.This judicious control enables a segmented growth,inducing the growth of insular nanocrystal consist of low-dimensional structure.Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%,ranking among the highest efficiency achieved.The homogeneous nano-island structure also enables high-efficiency large area(1 cm^(2))device up to 21.6%,and a record high value of 13.6%for highly semi-transparent ones.

High-member low-dimensional Sn-based perovskite solar cells

Sn-based perovskites are promising thin-film photovoltaic materials for their ideal bandgap and the eco-friendliness of Sn,but the performance of Sn-based perovskite solar cells is hindered by the short carrier diffusion length and large defect density in nominally-synthesized Sn-based perovskite films.Herein we demonstrate that a long carrier diffusion length is achievable in quasi-2D Sn-based perovskite films consisting of high-member low-dimensional Ruddlesden-Popper(RP)phases with a preferred crystal orientation distribution.The key to the film synthesis is the use of a molecular additive formed by phenylethylammonium cations and optimally mixed halide-pseudohalide anions,which favorably tailors the quasi-2D Sn-based perovskite crystallization kinetics.The high-member RP film structure effectively enhances device short-circuit current density,giving rise to an increased power conversion efficiency(PCE)of 14.6%.The resulting device demonstrates a near-unity shelf stability upon1,000 h in nitrogen.A high reproductivity is also achieved with a count of 50 devices showing PCEs within a narrow range from minimum 13.0%to maximum 14.6%.

Tin Halide Perovskite Solar Cells:An Emerging Thin-Film Photovoltaic Technology

Perovskite semiconductors are regarded as nextgeneration photovoltaic materials owing to their superb optoelectronic properties,including an excellent carrier diffusion length,strong light absorbption,low defect density,and solution processability.The PCE of lead perovskite solar cells(LPSC)rapidly increased from 3.8 to 25.5%in the past decade.However,the inclusion of soluble,toxic lead shadows its application due to environmental concerns.Furthermore,on the basis of the Shockley−Quisser(S−Q)limit,the efficiency of lead perovskite is limited to 32%since its band gap is>1.5 eV.To increase the efficiency of perovskite solar cells further,perovskite materials with a smaller band gap are required.Tin halide perovskite is currently the most promising alternative candidate that can address the above challenges due to its potentially less toxic character and electronic configuration analogous to that of lead.Its band gap(sub-1.4 eV)is lower than that of lead perovskite,approaching the ideal band gap with a theoretical efficiency of up to 33.4%based on the S−Q equation.However,tin perovskite is extremely easy to oxidize due to its unique electronic structure.Early works focus on the development of methods to reduce tin oxidation such as the addition of antioxidant additives or using low-dimensional structures.On the basis of these strategies,the reproducibility and efficiency of TPSCs have been significantly improved.In recent years,many works including composition engineering,functional additives,and device structure engineering have been used to improve the performance of TPSCs.On the basis of these strategies,the open-circuit voltage is improved to 0.94 V and the PCE certified by an independent laboratory is up to 12.4%.Meanwhile,the stability of TPSCs is significantly improved,and the stabilized power output time is up to 1000 h.Therefore,tin perovskite is emerging as a new generation of low-cost thin-film photovoltaic technology.This Account summarizes the properties of tin halide perovskites and the material and device engineering strategies toward more efficient and stable TPSCs.We highlight the unique properties of tin perovskites that distinguish them from lead perovskites,including their electronic structure,band structure,chemical properties,and so on.We discuss the critical challenges for the further development of TPSCs such as oxidation,high background carriers,uncontrollable crystallization,interface recombination,band alignment,and instability.In the end,we introduce potential directions for the future development of TPSCs including probing the formation mechanisms of tin perovskite,revealing the basic properties of Sn perovskite,overcoming the stability issue of TPSCs,and understanding TPSC device physics and structure engineering.

Hole-transporting layer-free inverted planar mixed lead-tin perovskite-based solar cells

Mixed lead-tin （Pb-Sn） perovskites present a promising strategy to extend the light-harvesting range of perovskite-based solar cells （PSCs）. The use of electron- transporting layer or hole-transporting layer （HTL） is critical to achieve high device efficiency. This strategy, however, requires tedious layer-by-layer fabrication as well as high-temperature annealing for certain oxides. In this work, we fabricated HTL-free planar FAPb0.5Sn0.5I3 PSCs with the highest efficiency of 7.94%. High short- circuit current density of 23.13 mA/cm2 was attained, indicating effective charge extraction at the ITO/ FAPb0.5Sn0.5I3 interface. This finding provides an alter- native strategy to simplify the manufacture of single- junction or tandem PSCs.

Molecularly manipulating orientation of hole transporting layers and mitigation of electrical loss for dopant-free CsPbI_(2)Br solar cells

Organo-lead halide perovskites(OHPs) possess superior optoelectronic properties and have achieved an amazing certified power conversion efficiency(PCE) of 25.5% in perovskite solar cells(PSCs)[1]. Recent studies revealed that the organic cations such as methylammonium(MA^(+)) and formamidinium(FA^(+)) and anions with weak electronegativity such as I^(-) in OHPs were causing instability.