Indium-gallium segregation in CuIn(x)Ga(1-x)Se2: an ab initio-based Monte Carlo study

Kesterite Solar Cells: Insights into Current Strategies and Challenges

Earth-abundant and environmentally benign kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is a promising alternative to its cousin chalcopyrite Cu(In,Ga)(S,Se)2 (CIGS) for photovoltaic applications. However, the power conversion efficiency of CZTSSe solar cells has been stagnant at 12.6% for years, still far lower than that of CIGS (23.35%). In this report, insights into the latest cutting-edge strategies for further advance in the performance of kesterite solar cells is provided, particularly focusing on the postdeposition thermal treatment (for bare absorber, heterojunction, and completed device), alkali doping, and bandgap grading by engineering graded cation and/or anion alloying. These strategies, which have led to the step-change improvements in the power conversion efficiency of the counterpart CIGS solar cells, are also the most promising ones to achieve further efficiency breakthroughs for kesterite solar cells. Herein, the recent advances in kesterite solar cells along these pathways are reviewed, and more importantly, a comprehensive understanding of the underlying mechanisms is provided, and promising directions for the ongoing development of kesterite solar cells are proposed.

Cluster expansion Monte Carlo study of indium–aluminum segregation and homogenization in CuInSe2–CuAlSe2 pseudobinary alloys

Systematic cluster expansion Monte Carlo simulations of CuIn_1−xAl_xSe₂ alloys probe the origin and evolution of In–Al segregation behavior comprehensively.

Nanoscopy of Phase Separation in InxGa1-xN Alloys

Phase separations in ternary/multinary semiconductor alloys is a major challenge that limits optical and electronic internal device efficiency. We have found ubiquitous local phase separation in In1-xGaxN alloys that persists to nanoscale spatial extent by employing high-resolution nanoimaging technique. We lithographically patterned InN/sapphire substrates with nanolayers of In1-xGaxN down to few atomic layers thick that enabled us to calibrate the near-field infrared response of the semiconductor nanolayers as a function of composition and thickness. We also developed an advanced theoretical approach that considers the full geometry of the probe tip and all the sample and substrate layers. Combining experiment and theory, we identified and quantified phase separation in epitaxially grown individual nanoalloys. We found that the scale of the phase separation varies widely from particle to particle ranging from all Ga- to all In-rich regions and covering everything in between. We have found that between 20 and 25% of particles show some level of Ga-rich phase separation over the entire sample region, which is in qualitative agreement with the known phase diagram of In1-xGaxN system.

Indium segregation measured in InGaN quantum well layer

The indium segregation in InGaN well layer is confirmed by a nondestructive combined method of experiment and numerical simulation, which is beyond the traditional method. The pre-deposited indium atoms before InGaN well layer growth are first carried out to prevent indium atoms exchange between the subsurface layer and the surface layer, which results from the indium segregation. The uniform spatial distribution of indium content is achieved in each InGaN well layer, as long as indium pre-deposition is sufficient. According to the consistency of the experiment and numerical simulation, the indium content increases from 16% along the growth direction and saturates at 19% in the upper interface, which cannot be determined precisely by the traditional method.

Composition- and band-gap-tunable synthesis of wurtzite-derived Cu₂ZnSn(S(1-x)Se(x))₄ nanocrystals: theoretical and experimental insights

The wurtzite-derived Cu₂ZnSn(S(1-x)Se(x))₄ alloys are studied for the first time through combining theoretical calculations and experimental characterizations. Ab initio calculations predict that wurtzite-derived Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ are highly miscible, and the band gaps of the mixed-anion alloys can be linearly tuned from 1.0 to 1.5 eV through changing the composition parameter x from 0 to 1. A synthetic procedure for the wurtzite-derived Cu₂ZnSn(S(1-x)Se(x))₄ alloy nanocrystals with tunable compositions has been developed. A linear tunable band-gap range of 0.5 eV is observed in the synthesized alloy nanocrystals, which shows good agreement with the ab initio calculations.