Charge carrier-selective contacts for nanowire solar cells

Abstract

Charge carrier-selective contacts transform a light-absorbing semiconductor into a photovoltaic device. Current record efficiency solar cells nearly all use advanced heterojunction contacts that simultaneously provide carrier selectivity and contact passivation. One remaining challenge with heterojunction contacts is the tradeoff between better carrier selectivity/contact passivation (thicker layers) and better carrier extraction (thinner layers). Here we demonstrate that the nanowire geometry can remove this tradeoff by utilizing a permanent local gate (molybdenum oxide surface layer) to control the carrier selectivity of an adjacent ohmic metal contact. We show an open-circuit voltage increase for single indium phosphide nanowire solar cells by up to 335 mV, ultimately reaching 835 mV, and a reduction in open-circuit voltage spread from 303 to 105 mV after application of the surface gate. Importantly, reference experiments show that the carriers are not extracted via the molybdenum oxide but the ohmic metal contacts at the wire ends.

SnO2-based electron transporting layer materials for perovskite solar cells: A review of recent progress

“…These local accumulations/inversions are caused by a difference in the Fermi level at the interface to establish carrier-selective contacts ( Fig. 3 ) [104] . In PSC devices, the difference between the Fermi level of the HTL and the ETL es-tablishes the built-in potential.…”

“…The role of the built-in potential is to separate the photon-generated electron and hole, which facilitates them to drift to the ETL and HTL, respectively. Once a suitable ETL material is found, it often has to be thin to reduce the resistance and absorption losses [104] . To achieve high-performance PSC devices, a uniform and thin SnO 2 film with low density of defects and pinhole-free is essential.…”

“…Schematic diagram of (a) heterojunction solar cells, (b) energy level and Fermi level (dark) of heterojunction solar cells[104] .…”

Exploring the Internal Radiative Efficiency of Selective Area Nanowires

“…In Figures 6(a) and 6(b), several different cleaning solutions are thus evaluated by measuring the integrated intensity of PL emission of intrinsic nanowires. SiO 2 deposited by PECVD at 300°C is used as passivation, as it has been demonstrated to be effective in several instances both for InP and for other III − V materials [15,16,18,49]. The use of SiO 2 only, without any cleaning beforehand, appears to be detrimental compared to the as-grown sample, most likely because without any cleaning the native oxide formed on the nanowire sidewalls prevents any effective passivation of the material.…”

“…They have been extensively studied in the last 10 years, with extremely promising results in lasing, transistor, and solar cell applications [12][13][14]. In particular, selective area InP nanowires have demonstrated very good PV device performance when measured in a single nanowire geometry [15,16].…”