Point defect engineering in thin-film solar cells

Abstract

Control of defect processes in photovoltaic materials is essential for realising high-efficiency solar cells and related optoelectronic devices. The concentrations of native defects and extrinsic dopants tune the Fermi level and enable semiconducting p-n junctions; however, fundamental limits to doping exist in many compounds. Optical transitions involving defect states can enhance photocurrent generation through sub-bandgap absorption; however, such states are often responsible for carrier trapping and non-radiative recombination events that limit open-circuit voltage. Many classes of materialsincluding metal oxides, chalcogenides, and halidesare being examined for next-generation solar energy applications, and each technology faces distinct challenges that could benefit from point defect engineering. We review the evolution in point defect behaviour from Si-based photovoltaics to thin-film CdTe and Cu(In,Ga)Se2 technologies, through to the latest generation halide perovskite (CH3NH3PbI3) and kesterite (Cu2ZnSnS4) devices. We focus on the chemical bonding that underpins the defect chemistry, and the atomistic processes associated with the photophysics of charge carrier generation, trapping, and recombination in solar cells. Finally, we outline general principles to enable defect control in complex semiconducting materials.

Reducing Detrimental Defects for High‐Performance Metal Halide Perovskite Solar Cells

“…As the fundamental origin, structural defects, and impurities in semiconductor materials play an important role in the overall performance of electronic devices in general . In several photovoltaic technologies (e.g., Si, CIGS, CdTe), the presence of electronic defects within the semiconductor band gap limits the efficiency, reproducibility, as well as stability/lifetime . Therefore, efforts have been made in the direction to minimize the defect density by well‐controlled semiconductor fabrication technology.…”

“…4) The fourth functionality is associated with the enlargement in grain size induced by the thiol groups. The growth of monolithic‐type and/or large perovskite grains in polycrystalline films is a widely employed strategy to reduce detrimental defects . Although several groups have reported that amino‐functionalized groups are efficient for passivating under‐coordinated PbI 6 octahedra (Table S2), Xu et al .…”

“…For example, grain boundaries lead to harmful deep levels in Si and CdTe, but they do not produce deep levels in CIGS, CZTSe, and CZTS materials. This is why passivation is critical in Si and CdTe solar cells, while passivation is less important in CIGS and CZTS solar cells . Organic semiconducting materials are more prone to the formation of trap states because of their disordered nature induced by the weak van der Waals interaction between molecules.…”

“…As a consequence, these defects play a similar important role in the performance of organic solar cells . Several Review articles provide insightful information about defects in Si, CdTe, CIGS, and organic based PV technologies …”

Defective [Bi2O2]2+ Layers Exhibiting Ultrabroad Near‐Infrared Luminescence

“…[1] In this pursuit, the incorporation of intrinsic or extrinsic atomic defects in structures that either exhibit naturally occurring vacancies or those with synthetically or postsynthetically introduced vacancies has been established as ap owerful approacht ot he finetuning of the properties of aw ide range of functional materials. Many of today's prominentm aterials, such as high-transition-temperature superconductors, [2,3] solar-drivenp hotocatalysts, [4][5][6][7] photovoltaic materials, [8] metal-organic frame-works, [9][10][11] and ferroelectrics, [12][13][14] are imperfect systems with defect-induced, locally broken periodic structures,i nw hich imperfection plays ap ivotal role in governing, or at least affecting, their physiochemicalproperties. [15][16][17][18][19][20] Materials consisting of as equence of infinitely repeating stacksof[Bi 2 O 2 ] 2 + layers,such as bismuth-based cupratesuperconductors, bismuth oxyhalides, and Aurivillius phases, have attracted intensivea ttention because they exhibit an array of tantalizing properties, such as superconductivity,p hotocatalytic, photoluminescence (PL),a nd ferroelectricity.…”