Optimizing the Back Contact of Kesterites and Perovskites: Band Edge Design and Defect Engineering in Molybdenum Chalcogenides

Abstract

Back contacts, as an important part of solar cell devices, play a critical role in efficient separation of carriers and reduction of interfacial recombination. Here, by analyzing interfacial band alignment, thickness and defect properties of back contacts, a design principle for back contacts is proposed to properly accommodate the interrelated factors of short‐circuit current (Jsc), open‐circuit voltage (Voc), series resistance (Rs), and nonradiative recombination centers (NRCs) at the same time. A preferred back contact should have (i) a high valance band maximum (VBM) and (ii) a low Fermi level relative to absorber to drive hole extraction and block electron leakage, (iii) a thin design under the premise of p+‐type characteristic to effectively reduce Rs, which also ensures a wide depletion region on the absorber side to promote hole collection, and (iv) no additional deep‐level defects as interfacial NRCs. Taking molybdenum chalcogenide as example, p+‐type MoSe2/MoS2 realized by group VB element doping satisfies the design principles and is promising as an excellent back contact for kesterite/perovskite solar cells. This study gives theoretical guidance for designing an ideal back contact and shows how to improve the photovoltaic performance of solar cells by interfacial optimization.

Flexible Transparent High‐Efficiency Photoelectric Perovskite Resistive Switching Memory

“…Built-in electric fields (E bi-ITO and E bi-Ag ) are formed, resulting in Schottky junction electrical characteristics or a Schottky barrier. [48,49] A contact resistance in the Schottky barrier is generated by the applied electric field. The width of the depletion regions increased or decreased when a bias (E bais ) is applied consistent with or opposite to the E bi-FTO or E bi-Ag direction, as shown in Figure 6c,d.…”

Synergetic Effects of Zn Alloying and Defect Engineering on Improving the CdS Buffer Layer of Cu2ZnSnS4 Solar Cells

“…Usually, element doping is an effective approach for improving the intrinsic weak conductivity by forming energetically favorable external defects. To form a strong built-in electric field and make most of it fall into the p-type CZTS side, dopants of In, Ga, and Cl are used to attempt to enhance the n-type conductivity of the Zn 0.25 Cd 0.75 S alloy according to the heterojunction band bending formula, 50 because their one more electron and approximate crystal ionic radius compared to the corresponding intrinsic cation and anion give priority to the formation of the n-type substitutional defects, such as the In Cd + , Ga Zn + , and Cl S + defects. Similar to that of the undoped Zn 0.25 Cd 0.75 S alloy, the upper limits of the chemical potential of In, Ga, and Cl are determined by avoiding the precipitation of the dopants and the secondary phases of their compounds (see the calculation details in part II of the Supporting Information), as plotted by the green, blue, and red lines in Figure 3a, respectively.…”

Analysis of Band Alignment Engineering and Interface Defects on a GaAs/GaSb Heterostructure Solar Cell

“…At the hetero interface, due to lattice mismatch, grain boundary defects like dangling bonds, TDs, and interface traps limit the performance of the device be deteriorating the V oc and J sc . [34][35][36][37][38] Trap centers, whose energy levels falls in the forbidden gap, exchange charge with the CB and VB through the emission and capture of electrons and holes. The trap centers influence the density of space charge in semiconductor and, hence, controls the V oc and J sc of the device as well.…”