Role of n-ZnO Layer on the Improvement of Interfacial Properties in ZnO/InGaN p-i-n Solar Cells

InGaN has been predicted to be an efficient photovoltaic material. However, the high-density polarization charges and large potential barrier at the i-InGaN/n-GaN interface create an electric field that severely decreases the collection efficiency of p-InGaN/i-InGaN/n-GaN heterostructure solar cells. We demonstrate that, according to numerical simulations, utilizing a p-InGaN/i-InGaN/n-ZnO heterostructure can greatly reduce the piezoelectric field in the absorption layer and reduce the potential barrier between the n-type layer and the absorption layer interface, thus improving the performances of the solar cell. Moreover, we studied the influence of the band alignment on the ZnO/InGaN interface on the performance of the solar cell. We found that the band alignment of the ZnO/InGaN interface can keep the solar cells at a very high efficiency over a wide scope. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon(a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure(HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT(heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD(heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells.The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 m A/cm^2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to(1) decrease of optical absorption loss of a-Si:H and(2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide(TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

Efficient emission of InGaN-based light-emitting diodes:toward orange and red

Indium gallium nitride(InGaN)-based light-emitting diodes(LEDs)are considered a promising candidate for red-green-blue(RGB)micro displays.Currently,the blue and green LEDs are efficient,while the red ones are inefficient for such applications.This paper reports our work of creating efficient InGaN-based orange and red LEDs on silicon(111)substrates at low current density.Based on the structure of InGaN yellow LEDs,by simply reducing the growth temperature of all the yellow quantum wells(QWs),we obtained 599 nm orange LEDs with peak wall-plug efficiency(WPE)of 18.1%at 2 A/cm^2.An optimized QW structure was proposed that changed two of the nine yellow QWs to orange ones.Compared with the sample containing nine orange QWs,the sample with two orange QWs and seven yellow QWs showed similar emission spectra but a much higher peak WPE up to 24.0%at 0.8 A/cm^2 with a wavelength of 608 nm.The improvement of peak WPE can be attributed to the improved QW quality and the reduced active recombination volume.Subsequently,a series of efficient InGaN-based orange and red LEDs was demonstrated.With further development,the InGaN-based red LEDs are believed to be attainable and can be used in micro LED displays.

Efficient InGaN-based yellow-light-emitting diodes

Realization of efficient yellow-light-emitting diodes(LEDs) has always been a challenge in solid-state lighting.Great effort has been made, but only slight advancements have occurred in the past few decades. After comprehensive work on InGaN-based yellow LEDs on Si substrate, we successfully made a breakthrough and pushed the wall-plug efficiency of 565-nm-yellow LEDs to 24.3% at 20 A∕cm^2 and 33.7% at 3 A∕cm^2. The success of yellow LEDs can be credited to the improved material quality and reduced compressive strain of InGaN quantum wells by a prestrained layer and substrate, as well as enhanced hole injection by a 3 D pn junction with V-pits.