Dopant‐free back contact silicon heterojunction solar cells employing transition metal oxide emitters

Abstract

The present study investigates the electrical properties of transition metal oxide (TMO) emitters in dopant‐free n‐Si back contact solar cells by comparing the properties of solar cells employing three TMOs (WOx, MoOx and V2Ox) with varying electrical properties acting as p‐type contacts. The TMOs are found to induce large band bending in n‐Si, which reduces the injection level dependent interfacial recombination speed Seff and contact resistivity ρc. Among the TMO/n‐Si contacts considered, the V2Ox/n‐Si contact achieves the lowest Seff of 138 cm/s and ρc of 0.034 Ω cm2, providing the significant advantages over heavily doped a‐Si:H(p)/n‐Si contacts. The best device performance was achieved by the V2Ox/n‐Si solar cell, demonstrating an efficiency of 16.59% and an open‐circuit voltage of 610 mV relative to solar cells based on MoOx/n‐Si (15.09%, 594 mV) and WOx/n‐Si (12.44%, 539 mV). Furthermore, the present work is the first to employ WOx, V2Ox and Cs2CO3 in back contact solar cells. The fabrication process employed offers great potential for the mass production of back contact solar cells owing to simple, metal mask patterning with high alignment quality and dopant‐free steps conducted at a lower temperature.

Recent Advances in and New Perspectives on Crystalline Silicon Solar Cells with Carrier-Selective Passivation Contacts

“…Alternative materials are expected to completely replace doped silicon layers to form the asymmetric carrier selective heterocontacts with c-Si wafers. These alternative materials, which usually are called carrier-selective materials or passivation contact materials, include transition metal oxides [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], organic materials [48][49][50][51][52][53], and alkali/alkaline earth metals and/or salts [30,40,[54][55][56][57][58][59][60][61]. Compared to doped-silicon layers, dopant-free carrier-selective materials open a wider optical and electrical parameter space, decoupling the optimization of different solar cell loss components.…”

“…For example, electron-selective contacts include compounds with a low work function, such as LiF x [30,32,40], MgF x [56], TiO 2 [31,40,[43][44][45] and ZnO [46,47], and alkaline metals with an extremely low work function, such as Mg [54] and Ca [57]. Hole-selective contacts mainly consist of organic films [48][49][50][51][52][53] and transition metal oxides (TMO s ), such as MoO x [30,32,[36][37][38][40][41][42]47], WO x [35,38,39] [33][34][35]38], and NiO x [31].…”

“…If both the dopant-free hole and electron-selective contacts are deposited on the front and rear sides of c-Si wafers, respectively, these novel devices are nominated as dopant-free asymmetric heterocontacts (DASH) solar cells [30,40], which have been widely investigated in recent years and will be one of the most promising key issues for further improving the performance of c-Si-based solar cells. The DASH solar cells, based on TMOs, have the following advantages [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]: (1) TMOs have a large band gap and thus low parasitic light absorption, which is beneficial for increasing the short-circuit current density of the solar cell; (2) the DASH solar cell has a very high efficiency potential of up to 28% [31]; (3) most of the TMOs can be deposited by low-temperature and low-cost techniques, such as thermal evaporation or the solution method; (4) no flammable, explosive, or toxic gases and materials are used; (5) it is easy to realize the IBC structure by multi-step masks, which avoids the complicated photolithography processes [32][33][34].…”

“…Gerling [38] and Wu [39] compared the effects of the V 2 O x , MoO x , and WO x hole-selective contacts on the SHJ solar cells, reaching a conclusion that V 2 O x is a better candidate for the hole-selective contact. Shen and co-workers proposed a multi-layered emitter (i.e., hole-selective contact) based on a TMO/Ag/TMO structure [33,81].…”

Analysis of temperature dependent current-voltage and capacitance-voltage characteristics of an Au/V2O5/n-Si Schottky diode

“…Therefore, it has emerged as one of the most important semiconductors for different device applications namely, organic light emitting diodes, 11 photogenerated charges, 12 organic field effect transistors, 13 gas sensors, 14 Schottky diodes 15 and especially in photovoltaics. 16,17 In recent work,V 2 O 5 thin films have been used as hole conducting buffer layers for heterojunction solar cell and interdigited back contacted solar cells that achieved 15.7% and 19.7% conversion efficiency respectively. 18,19 However, room temperature current-voltage measurements are not sufficient to fully understand the current conduction phenomenon through the V 2 O 5 layer.…”