Abstract
Research on photovoltaic devices with a high performance-to-cost ratio requires efforts not only on efficiency improvement but also on manufacturing cost reduction. Recently, a record efficiency of 26.6% on crystalline silicon solar cells (SCs) has been achieved by combining the heterojunctions (HJs) with a device structure of interdigitated back contacts. However, the technology that integrates the interdigital p- and n-type amorphous silicon (a-Si:H) layers on the rear surface of the Si substrate is challenging. This issue has motivated researchers to search dopant-free carrier-selective contacts with alternative materials to completely replace doped a-Si:H layers. Transition metal oxides, graphene, and poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), all having high work functions and hole conducting properties, can play the role of hole-selective layers (HSLs). In this review, we focus on the latest advances and the future trends in these HSLs and their applications in silicon HJ SCs. The main issues and challenges encountered are discussed.
Highlights
As a promising alternative technique to crystalline silicon solar cells (SCs) for a higher performance-to-cost ratio, passivation contacts [ known as heterocontacts or carrier selective contacts (CSCs)] attract ever-increasing interest
These results further indicate that the high work function of transition metal oxides (TMOs) is critical to improving the performance of TMO/Si solar cells
Recent studies indicated that the performance of heterojunction solar cells (HSCs) with transparent conductive oxide (TCO)/MoOx/amorphous silicon (a-Si):H(i) stacks degraded after annealing at temperatures from 130 ○C to 200 ○C, i.e., FF dropped from 76.6% to 69.7%14 or peak-to-correlation energy (PCE) dropped from 12.6% to 11%9 because of hydrogen diffusion
Summary
As a promising alternative technique to crystalline silicon (cSi) solar cells (SCs) for a higher performance-to-cost ratio, passivation contacts [ known as heterocontacts or carrier selective contacts (CSCs)] attract ever-increasing interest. The TiOx layer is often used as an electron selective contact due to a very small conduction band offset (about 0.05 eV) and a large valence band offset (>2.0 eV) at the n-Si/TiOx interface.[1] Recently, c-Si solar cells with a record efficiency of 24.4% (module, double-sided junctions)[2] and 26.6% [laboratorial, interdigitated back contact (IBC) structure]3 have been achieved, largely owing to the application of passivation contacts In these two types of devices, intrinsic hydrogenated amorphous silicon [a-Si:H(i)] was used to passivate the Si surface and p/n-type doped hydrogenated amorphous silicon [a-Si:H(p)/a-Si:H(n)] was employed to deliver carrier-selective transport. Attention will be emphasized on the latest advances in the modification of HSL materials, interfacial passivation, contact resistivity, and device structures
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