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.

Among new flexible transparent conductive electrode (TCE) candidates, ultrathin Ag film (UTAF) is attractive for its extremely low resistance and relatively high transparency. However, the performances of UTAF based TCEs critically depend on the threshold thickness for growth of continuous Ag films and the film morphologies. Here, we demonstrate that these two parameters could be strongly altered through the modulation of substrate surface energy. By minimizing the surface energy difference between the Ag film and substrate, a 9 nm UTAF with a sheet resistance down to 6.9 Ω sq−1 can be obtained using an electron-beam evaporation process. The resultant UTAF is completely continuous and exhibits smoother morphologies and smaller optical absorbances in comparison to the counterpart of granular-type Ag film at the same thickness without surface modulation. Template-stripping procedure is further developed to transfer the UTAFs to flexible polymer matrixes and construct Al2O3/Ag/MoOx (AAM) electrodes with excellent surface morphology as well as optical and electronic characteristics, including a root-mean-square roughness below 0.21 nm, a transparency up to 93.85% at 550 nm and a sheet resistance as low as 7.39 Ω sq−1. These AAM based electrodes also show superiority in mechanical robustness, thermal oxidation stability and shape memory property.

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PFN is introduced to the Al/n-Si interface to improve the contact quality by reducing the work function of Al electrode, getting an ohmic contact. An excellent photovoltaic efficiency of 13.35% has been achieved in a planar device with a PFN layer.

Carrier collection in conventional n‐type Si (n‐Si)/organic hybrid heterojunction solar cells (HHSCs) is mainly limited by the nonoptimized top grid‐electrode and inadequate work function (WF) of the PH1000‐type poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Here, a novel modified metal polymer nanocomposite top electrode (M‐MPNTE) is designed to achieve a full‐area carrier collection in n‐Si/PEDOT:PSS HHSCs. The carrier collection in both lateral and vertical directions is significantly improved by the introduction of an ultrathin Au/MoOx modified layer between 6 nm ultrathin Ag film and AI4083‐type PEDOT:PSS layer. In addition, the carrier separation is boosted by the enhanced built‐in potential owing to a high WF of M‐MPNTE, which also suppresses the carrier recombination at the surface of n‐Si. Due to these collaborative improvements, a record fill factor of 80.21% is obtained, which is even comparable to the best value of the traditional Si‐based solar cells. With the addition of a MoOx antireflective coating layer on top of M‐MPNTE, the short‐circuit current density and open‐circuit voltage are finally increased to 23.13 mA cm−2 and 621.07 mV, respectively, yielding a power conversion efficiency of 10.82%. The finding suggests a novel strategy for the development of highly efficient HHSCs with ideal carrier transport mechanism.

Back contact property plays a key role in the charge collection efficiency of c-Si/poly(3,4-ethylthiophene):poly(styrenesulfonate) hybrid solar cells (Si-HSCs), as an alternative for the high-efficiency and low-cost photovoltaic devices. In this letter, we utilize the water soluble poly (ethylene oxide) (PEO) to modify the Al/Si interface to be an Ohmic contact via interface dipole tuning, decreasing the work function of the Al film. This Ohmic contact improves the electron collection efficiency of the rear electrode, increasing the short circuit current density (Jsc). Furthermore, the interface dipoles make the band bending downward to increase the total barrier height of built-in electric field of the solar cell, enhancing the open circuit voltage (Voc). The PEO solar cell exhibits an excellent performance, 12.29% power conversion efficiency, a 25.28% increase from the reference solar cell without a PEO interlayer. The simple and water soluble method as a promising alternative is used to develop the interfacial contact quality of the rear electrode for the high photovoltaic performance of Si-HSCs.

Poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS)/Si hybrid heterojunction solar cells (HHSCs) have attracted wide interests due to the potential high efficiency and low cost, but their open circuit voltage is limited. Here, double-layered PEDOT:PSS films (DL-PEDOT:PSS), high-work-function AI4083-type PEDOT:PSS (HW-PEDOT:PSS) used to combine with high-conductivity PH1000-type PEDOT:PSS (HC-PEDOT:PSS), were applied to induce strong inversion layers at the n-type silicon surface in PEDOT:PSS/Si HHSCs resulting in a quasi-p–n junction. Capacitance–voltage and minority carrier lifetime mapping demonstrates that the quasi-p–n junction was formed by strong inversion effect with large built-in voltage. The device with DL-PEDOT:PSS with 7 wt % EG added in HW-PEDOT:PSS (EG7-DL-PEDOT:PSS) exhibits a large open circuit voltage of 640 mV without any other modification, fill factor of 0.755, and power conversion efficiency of 12.69%. This suggests a promising method for the fabrication of low-cost and high-performance PEDOT:PSS/Si HHSCs, as well as a p-type passivated contact in the next-generation solar cells.

The internal resistance and capacitance of Si/organic hybrid solar cells (Si-HSC) based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are investigated by electrochemical impedance spectroscopy (EIS). Three types of Nyquist plots in Si-HSC are observed firstly at different bias voltages, while suitable equivalent circuit models are established to evaluate the details of interface carrier transfer and recombination. In particular, the carrier transport property of the PEDOT:PSS film responds at a high frequency (6 × 104–1 × 106 Hz) in three-arc spectra. Therefore, EIS could help us deeply understand the electronic properties of Si-HSC for developing high performance devices.