Dopant‐Free and Carrier‐Selective Heterocontacts for Silicon Solar Cells: Recent Advances and Perspectives

Abstract

By combining the most successful heterojunctions (HJ) with interdigitated back contacts, crystalline silicon (c‐Si) solar cells (SCs) have recently demonstrated a record efficiency of 26.6%. However, such SCs still introduce optical/electrical losses and technological issues due to parasitic absorption/Auger recombination inherent to the doped films and the complex process of integrating discrete p+‐ and n+‐HJ contacts. These issues have motivated the search for alternative new functional materials and simplified deposition technologies, whereby carrier‐selective contacts (CSCs) can be formed directly with c‐Si substrates, and thereafter form IBC cells, via a dopant‐free method. Screening and modifying CSC materials in a wider context is beneficial for building dopant‐free HJ contacts with better performance, shedding new light on the relatively mature Si photovoltaic field. In this review, a significant number of achievements in two representative dopant‐free hole‐selective CSCs, i.e., poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate)/Si and transition metal oxides/Si, have been systemically presented and surveyed. The focus herein is on the latest advances in hole‐selective materials modification, interfacial passivation, contact resistivity, light‐trapping structure and device architecture design, etc. By analyzing the structure–property relationships of hole‐selective materials and assessing their electrical transport properties, promising functional materials as well as important design concepts for such CSCs toward high‐performance SCs have been highlighted.

Photon management effects of hybrid nanostructures/microstructures for organic-silicon heterojunction solar cells

“…Presently, silicon-based solar cells, which occupy over 90% market share, are the mainstream products in the commercial photovoltaic market owing to their nontoxicity, material abundance, high reliability, acceptable efficiency, long-term stability, and mature fabrication technologies. 1 Recently, the record efficiency of the crystalline silicon (c-Si) homojunction solar cells is 25.1% while that of heterojunction solar cells reaches to 26.6%, which are very close to the theoretical limit 29.4%. [2][3][4][5] However, these traditional silicon solar cells require complex fabrication process, and their costs are very expensive, impeding their large-scale applications at present.…”

“…Photovoltaic cell, a pollution‐free green energy resource, is considered as a promising way to mitigate the energy crisis and environmental pollution. Presently, silicon‐based solar cells, which occupy over 90% market share, are the mainstream products in the commercial photovoltaic market owing to their nontoxicity, material abundance, high reliability, acceptable efficiency, long‐term stability, and mature fabrication technologies . Recently, the record efficiency of the crystalline silicon (c‐Si) homojunction solar cells is 25.1% while that of heterojunction solar cells reaches to 26.6%, which are very close to the theoretical limit 29.4% .…”

Conductive Hole‐Selective Passivating Contacts for Crystalline Silicon Solar Cells

“…This is why a conductive passivation material has eluded researchers so far. Thus, although a host of previous work focus on the PEDOT:PSS/c‐Si heterojunction solar cells, such as organic−inorganic hybrid cells [ 24,31–34 ] and the BackPEDOT concept developed by Schmidt et al [ 35–38 ] has already presented the emphasis on hole selectivity and not passivation.…”

Highly Conductive and Wettable PEDOT:PSS for Simple and Efficient Organic/c‐Si Planar Heterojunction Solar Cells

“…Organic/c‐Si hybrid heterojunctions comprising a silicon‐based absorber and an organic carrier‐selective functional layer are promising materials for manufacturing low‐cost fabrication and high power conversion efficiency (PCE) next‐generation photovoltaic (PV) cells, because of the many unique properties of c‐Si and simple device structure . Nonetheless, organic semiconductors associated with nonideal interfacial contacts and low electrical conductivity can considerably impede the improvement of device performance for planar heterojunction solar cells.…”

“…Poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) polymer is considered to be one of the most realistic candidates as the hole‐selective functional layer for organic and perovskite solar cells, due to its high transparency and tunable optoelectronic properties . However, pristine PEDOT:PSS (4083, PH‐1000) film has a conductivity below 10 S cm −1 , much too low to be used as a carrier‐selective and collecting functional layer without a transparent conductive electrode in an efficient organic/c‐Si hybrid heterojunction solar cell …”