Properties Of Heterojunction Solar Cells Research Articles

Integration of thin n-type nc-Si:H layers in the window-multilayer stack of heterojunction solar cells

N-type nanocrystalline silicon (nc-Si:H(n)) layers are good candidates to improve current and transport properties in heterojunction solar cells. In this work, we perform thickness series alongside PH 3 doping series to unravel the desirable characteristics of nc-Si:H(n) along its growth direction. While increasing the PH 3 flow is necessary to improve the conductivity of the layer, we observe that too high flows lead to an amorphization of the first 10–15 nm of the layers. In consequence, either high crystallinity are reached at intermediate PH 3 flow, resulting in high doping at the n/TCO interface but a poorly doped nucleation zone, or the material becomes more amorphous at very high PH 3 flow, allowing a higher doping in the nucleation zone but a less efficient screening of the barrier with the TCO due to the lower crystallinity. To overcome this trade-off, we integrate a 2.5 nm a-Si:H(n) layer underneath the nc-Si:H(n) layer. We also report on the impact of higher ITO doping as well as on the beneficial effect of an additional SiO x capping not only to form a double anti-reflective coating (DARC), but also to improve contact properties. We observe that each of those three features can improve passivation and selectivity as well as reduce strongly the front contact resistivity ( ρ c ). Our best results are achieved by using a thin a-Si:H(n)/nc-Si:H(n) stack together with an IZrO/SiO x DARC, enabling front ρ c lower than 15 mΩ cm 2 and an efficiency of 23.7% on screen-printed 2 × 2 cm 2 solar cells. • Development of nc-Si :H(n) layers for front application. • Trade-off between nucleation zone and high crystallinity evidenced. • a-Si:H(n)/nc-Si:H(n) bilayer strategy allow for ρ c ¡ 15 mΩ cm 2 . • Decreases dependency upon TCO lateral conductivity. • Good passivation (pFF = 85%) and transparency maintained.

Retraction: Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells.

Retraction of 'Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells' by Xiangyang Liu et al., Phys. Chem. Chem. Phys., 2016, 18, 24299-24306.

Correction: Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells.

Correction for 'Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells' by Xiangyang Liu et al., Phys. Chem. Chem. Phys., 2016, 18, 24299-24306.

Heterojunction Solar Cells Fabricated with a Cu2o:Mn Thin Film Grown Epitaxially on p-Type Cu2o:Na Sheets By Electrochemical Deposition

This paper describes the effect of inserting a impurity-doped Cu2O thin-film buffer layer on the obtainable photovoltaic properties in heterojunction solar cells. The heterojunction solar cells were fabricated by preparing an n-type oxide semiconductor thin-film window layer on a Cu2O homojunction that was formed by epitaxially growing the doped Cu2O thin film buffer layer on p-type Cu2O sheets by electrochemical deposition (ECD). The doped Cu2O thin film buffer layer, incorporating various impurities, was prepared on thermally oxidized polycrystalline p-type sodium-doped Cu2O (p-Cu2O:Na) sheet substrates under various deposition conditions using the following ECD process. Initially, an acetic acid and Copper (II) acetate aqueous solution was prepared with 0.08 M acetic acid, 0.02 M Copper (II) acetate and de-ionized water; then a 0.1-1.0×10-5 M InCl3, CdCl2, ZnCl2 or MnCl2 aqueous solution was added to the solution as a doping impurity; and after that, a 3 M LiOH, NaOH or KOH aqueous solution was added to adjust the pH. Next, a p-Cu2O:Na sheet substrate was immersed in the above solution at a temperature of 60-90 oC; a Pt plate and the p-Cu2O:Na sheet substrate were used as the anode and cathode electrodes, respectively, of the ECD. Finally, the deposition was carried out under various current densities of 0.1-2.0 mA/cm2 for durations of 1-30 min. Various n-type GaXAl1-X-O or Zn1-XGeX-O multicomponent oxide thin films and an Al-doped ZnO (AZO) thin film were deposited at room temperature using a pulsed laser deposition as the n-type semiconductor layer and the transparent electrode, respectively. The solar cells were fabricated by forming an AZO/n-oxide semiconductor/doped Cu2O/p-Cu2O:Na structure on the front surface of the Cu2O:Na sheets and an Au ohmic electrode on the back surface (the sheets function as the active layer as well as the substrate). The photovoltaic properties of the resulting solar cells were measured under AM1.5G solar illumination. The Cu2O homojunction was formed by epitaxially growing a doped Cu2O thin film on p-Cu2O:Na (with a hole concentration of 1015-1019 cm-3) sheets by ECD. Significantly enhanced open circuit voltage (VOC) and conversion efficiency (η) were achieved in AZO/Ga0.98Al0.02-O/Cu2O:Mn/p-Cu2O:Na heterojunction solar cells fabricated by inserting a Mn-doped Cu2O (Cu2O:Mn) thin-film as the buffer layer with an appropriate thickness using ECD; these values were higher than those obtained in AZO/Cu2O:Mn/p-Cu2O and AZO/Ga0.98Al0.02-O/p-Cu2O solar cells. The obtained enhanced Voc and η suggest that the Cu2O:Mn thin-film buffer layer has excellent crystallinity as well as acts as an appropriate active layer. In addition, significant improvement of photovoltaic properties was achieved in heterojunction solar cells fabricated with a GaXAl1-X-O or Zn1-XGeX-O multicomponent oxide thin film n-type semiconductor window layer prepared by optimizing the chemical composition (the Ga or Ge content). Note that the photovoltaic properties obtained in AZO/Ga0.98Al0.02-O or Zn0.28Ge0.62-O/Cu2O:Mn/p-Cu2O:Na (with a hole concentration on the order of 1015 cm-3) heterojunction solar cells could be controlled by changing the Mn content doped into the Cu2O:Mn thin film. An efficiency over 8% was obtained in an AZO/ Zn0.28Ge0.62-O/Cu2O:Mn/p-Cu2O:Na heterojunction solar cell fabricated with a Cu2O:Mn thin film that was identified as an i-type semiconductor.

Opto-electronic properties of a TiO2/PS/mc-Si heterojunction based solar cell

In this work, we show the results of our investigation on the photoelectric properties of heterojunction solar cells based on Au/PS/mc-Si/Al and Au/TiO2/PS/mc-Si/Al structures. Porous silicon (PS) were prepared by an electrochemical etching process with different values of current density. The surface porosity was found to increase with the increase of current density. Pulsed laser deposition was used to deposit 80nm TiO2 thin films. Surface morphology and structural properties of TiO2/PS were characterized by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An enhancement of the electrical properties of the TiO2/PS/mc-Si heterojunction was observed after coating with TiO2. As a consequence, the solar cell efficiencies increased from 1.4% for the uncoated PS/mc-Si structure to 5% for the TiO2 coated one. Impedance spectroscopy confirmed the passivation effect of TiO2 through the improvement of the elaborated cells’ electron lifetime and the formation of a TiO2/PS/Au heterojunction with the appearance of a second semi-circle in the Nyquist plot.

Comprehensive insights into the charge dynamics process and excellent photoelectric properties of heterojunction solar cells.

Zn2SnO4 octahedron nanoparticles/Cu4Bi4S9 (ZTO/CBS) and ZTO octahedron nanoparticles/CBS-graphene nanoplatelets (ZTO/CBS-GNs), as well as two types of bulk heterojunction (BHJ) solar cells with high flexibility were prepared on stainless steel meshes (SSMs). The improved photovoltaic responses of CBS-GNs and ZTO/CBS-GNs with the incorporation of graphene nanoplatelets were determined using surface photovoltage spectroscopy (SPS). The signals of time-resolved fluorescence response (TFR) and transient surface photovoltage (TPV) can provide more detailed information on the transition, separation and transport of photogenerated carriers. Here, the ZTO/CBS-GNs cell exhibits a superior performance and the highest efficiency is 8.6%. The multichannel separation process from the TPV signals indicates that the macro-photoelectric signals can be attributed to photogenerated charges separated at the interface of CBS/GNs, rather than CBS/ZTO. The comprehensive signals of SPS, TFR and TPV not only provide insights into the transition, separation and shifting of photogenerated carriers, but also promote the exploration of charge dynamics from the picosecond to second range. Importantly, the BHJ flexible solar cells with excellent efficiency and facile, scalable production present significant potential for practical application.

Relationship between the electrical properties of the n-oxide and p-Cu2O layers and the photovoltaic properties of Cu2O-based heterojunction solar cells

We investigated the relationship between the electrical properties (of the n-oxide semiconductor layer and the p-Cu2O sheet) and the obtainable photovoltaic properties of Al-doped ZnO (AZO)/n-oxide/p-Cu2O heterojunction solar cells that were fabricated using either p-type non-doped Cu2O or Na-doped Cu2O (Cu2O:Na) sheets (prepared by thermally oxidizing a Cu sheet) functioning as the active layer as well as the substrate. We fabricated some heterojunction solar cells using p-Cu2O (non-doped) sheets and n-ZnO thin films with various electron concentrations (N) in the range of 1017―1020cm−3; non-doped and Al- or Cu-doped ZnO thin films were deposited under various O2 or O3 gas atmosphere pressures using a pulsed laser deposition (PLD) method. The obtained photovoltaic properties exhibited a tendency to increase as N was increased from 1017 to about 3×1019cm−3; the values remained at these maximum levels as N was increased to about 8×1019cm−3, and then they decreased as N was increased further. With an N on the order of 1020cm−3, the reduction of photovoltaic properties was attributed to an increase in the discontinuity of the conduction band at the interface between the n-ZnO and p-Cu2O layers. In addition, we found that the hole concentration (P) in Cu2O:Na sheets (i.e., Cu2O sheets postannealed with various Na compounds) could be controlled in the range of 1014―1019cm−3 by varying the annealing temperature and duration. As another example, the obtained photovoltaic properties in heterojunction solar cells that were fabricated by depositing n-(Ga0.975Al0.025)2O3 thin films on p-Cu2O:Na sheets by PLD remained constant as P was increased to approximately 1×1016cm−3, and then they decreased significantly as P was increased further. The reduction of the obtained photovoltaic properties in heterojunction solar cells fabricated using Cu2O:Na sheets with a P above about 1.4×1016cm−3 was attributed mainly to decreases of both the depletion layer width and the diffusion length.