Mitigating Plasmonic Absorption Losses at Rear Electrodes in High‐Efficiency Silicon Solar Cells Using Dopant‐Free Contact Stacks

Abstract

Although charge-carrier selectivity in conventional crystalline silicon (c-Si) solar cells is usually realized by doping Si, the presence of dopants imposes inherent performance limitations due to parasitic absorption and carrier recombination. The development of alternative carrier-selective contacts, using non-Si electron and hole transport layers, has the potential to overcome such drawbacks and simultaneously reduce the cost and/or simplify the fabrication process of c-Si solar cells. Nevertheless, devices relying on such non-Si contacts with power conversion efficiencies (PCEs) that rival their classical counterparts are yet to be demonstrated. In this study, one key element is brought forward toward this demonstration by incorporating low-pressure chemical vapor deposited ZnO as the electron transport layer in c-Si solar cells. Placed at the rear of the device, it is found that rather thick (75 nm) ZnO film capped with LiF x /Al simultaneously enables efficient electron selectivity and suppression of parasitic infrared absorption. Next, these electron-selective contacts are integrated in c-Si solar cells with MoO x -based hole-collecting contacts at the device front to realize full-area dopant-freecontact solar cells. In the proof-of-concept device, a PCE as high as 21.4% is demonstrated, which is a record for this novel device class and is at the level of conventional industrial solar cells.

Stable MoOX‐Based Heterocontacts for p‐Type Crystalline Silicon Solar Cells Achieving 20% Efficiency

“…After inserting the ITO layer, the parasitic aborption of Ag ( Figure S3b, Supporting Information) and MoO X ( Figure S3c, Supporting Information) in the wavelength range of 1030-1100 nm are depressed, while an additional absorption from ITO layer ( Figure S3d, Supporting Information) is seen due to its free carrier absorption in the infrared range. [7] The absorptions of both SiO X and V 2 O X are below 5 × 10 −14 % because of their low extinction coefficient. [59,60] The equivalent current density (J eq ) in bulk Si and each individual functional layer at rear side with diffferent contact configurations are further quantitatively evaluated.…”

“…[5] The HIT solar cells also suffer a high parasitic absorption arising from the a-Si:H and transparent conductive oxide (TCO) layers. [6,7] With the aim of further boosting the efficiency with a lower cost, a variety of transition metal compounds have been adopted as carrier-selective contacts (CSCs) for c-Si heterojunction solar cells. The transition metal oxides (TMOs) with large work functions (>5.5 eV), such as MoO X , [8][9][10][11] [12][13][14][15] and WO X, [16][17][18] can induce an accumulation of holes in p-type silicon (p-Si) [8] or depletion of electrons in n-type silicon (n-Si), [19] thus benefiting the hole transport.…”

Evaluating Materials Design Parameters of Hole-Selective Contacts for Silicon Heterojunction Solar Cells

“…This formation may cause a trapping layer, leading to increased D it and other effects. However, as shown recently, it is also possible that SiO x is forming at the interface without a significant detrimental effect on passivation [62]. In fact, Nayak et al reported that an intentionally introduced SiO x layer actually improves the solar cell performance in (n) c-Si / (i) SiO x / (p) NiO x devices [22].…”

Recombination junctions for efficient monolithic perovskite-based tandem solar cells: physical principles, properties, processing and prospects

“…25 Moreover, with well-designed transparent electrodes (usually transparent conductive oxides, TCOs) at their front and rear, SHJ cells feature high external quantum efficiencies (EQEs) for long-wavelength photons, thanks to their displaced-metal rear contact structure and the possibility to employ dopant-free junctions. 26 For these reasons, they may be regarded as ideal bottom cell partner in silicon-based tandems, 27 and have indeed been employed for most high-efficiency perovskite/ silicon tandems to date. According to the polarity of the tandem, these silicon films can -at least in principle -be coupled either as Si(n + ) with the perovskite HTL or as Si(p + ) with the perovskite ETL, resulting respectively in Si(n + )/HTL and Si(p + )/ETL hybrid RJs.…”