Solution‐Processed Copper‐Doped Chromium Oxide with Tunable Oxygen Vacancy for Crystalline Silicon Solar Cells Hole‐Selective Contacts

Abstract

Compared with vacuum evaporation, metal oxides deposited by solution process exhibit advantages, for example, dopants can be easily incorporated in a wide range and the contents are easy to be regulated by changing the composition of precursors. Herein, solution‐processed p‐type copper‐doped chromium oxide (Cu:CrOx) films with tunable oxygen vacancy are demonstrated via a postannealing process. The synthetic and postannealing temperature have a significant impact on the chromium cation oxidation state in the Cu:CrOx films, leading to the variation of work function for the oxide films. By adjusting the work function of Cu:CrOx films, a low contact resistivity of 95 mΩ cm2 can be realized for the Ag/Cu:CrOx/p‐Si contact. Finally, the optimized Cu:CrOx films are used as the hole transporting layer in c‐Si solar cells, showing an increased power conversion efficiency from 15.2% (without Cu:CrOx) to 16.9% (with Cu:CrOx). The results show an effective stage to use p‐type metal oxides as a hole‐selective layer in c‐Si solar cells.

Carrier‐selective contacts using metal compounds for crystalline silicon solar cells

“…A work function of 4.8 eV was obtained, probably limited by reduction with H and presence of the Cr 2‐x O 3 phase. Recently, Xu et al 256 processed aqueous solution of a copper doped chromium oxide (mixed phase of Cr 2‐x O 3 , Cr (OH) 3 , CrO 3‐x and CrO 2 ), spin‐coated at the rear side of p‐type Si absorber, post annealed at 150°C. They obtained a work function of 5.04 eV for the films, and solar cell efficiency of 16.6% (15.9% without Cu doping).…”

Tunable Hole‐Selective Transport by Solution‐Processed MoO3−x Via Doping for p‐Type Crystalline Silicon Solar Cells

“…TMOs with high work function (>5.5 eV) have been widely used for the hole-selective contact layers of c-Si heterojunction solar cells, such as molybdenum oxide (MoO 3Àx , x < 3), [13] vanadium oxide (V 2 O 5Àx ), [14] tungsten oxide (WO 3Àx ) [15] and chromium oxide (CrO 3Àx ). [16] These TMO/c-Si heterojunctions induce the accumulation of holes or the depletion of electrons, achieving the highly selective transport of holes. [17] In 2014, Javey's group first used MoO 3Àx as the hole-selective contact layer of n-type SHJ solar cell and obtained a conversion efficiency of 14.3%.…”

Greatly enhanced hole collection of MoOx with top sub-10 nm thick silver films for gridless and flexible crystalline silicon heterojunction solar cells

“…Otherwise, the ll factor (FF) of the cell becomes quite low even with dense Ag grids directly on top of the TMO. 49 For those TMO/TCO-based HSCs, a Ag grid electrode is indispensable, 22,25,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] inevitably shading part of the sunlight and decreasing the absorption and thus the J sc . It is also known that indium is scarce and TCOs containing indium have been increasing in price, especially ITO.…”

“…TMO-based HSCs are oen used as front contacts of solar cells. 22,25,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] Due to their rather poor conductivity, TMOs have to be capped with transparent conductive oxides (TCOs), 22,25,26,[28][29][30] such as indium tin oxide (ITO) and hydrogenated indium oxide, to improve their carrier transport and collection efficiency. Otherwise, the ll factor (FF) of the cell becomes quite low even with dense Ag grids directly on top of the TMO.…”

“…29 and 42–45) and CrO x . 46 Based on undoped inorganic HSCs and ESCs, the PCEs of c-Si heterojunction solar cells have exceeded 20%. 47,48 Meanwhile, these dopant-free heterocontacts can be processed easily under low temperatures, and the PV cost can be reduced further.…”